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Q1. Chemical properties of isotopes of an element are:
Chemical properties of isotopes of an element are the same because they have the same number of electrons and the same electronic configuration. Isotopes differ only in the number of neutrons, which does not affect their chemical behaviour. The chemical properties depend on the valence electrons, which are identical for isotopes.
Q2. An isotope of cobalt is used in:
An isotope of cobalt (cobalt-60) is used in the treatment of cancer. It is a radioactive isotope that emits gamma rays, which can be used to destroy cancer cells. This is known as radiotherapy or radiation therapy.
Q3. The mass of an electron is approximately:
The mass of an electron is approximately 1/2000 of the mass of a hydrogen atom. More precisely, it is about 1/1836 of a proton. This means electrons have negligible mass compared to protons and neutrons.
Q4. Deuterium (D) has number of neutrons:
Deuterium (D) has 1 neutron. It is an isotope of hydrogen with atomic number 1 and mass number 2. Since it has 1 proton, the number of neutrons = mass number – atomic number = 2 – 1 = 1. Deuterium is also called “heavy hydrogen.”
Q5. Atoms of different elements with same mass number are called:
Atoms of different elements with the same mass number are called isobars. For example, calcium-40 (Z=20) and argon-40 (Z=18) have the same mass number (40) but different atomic numbers. They have different numbers of protons and neutrons.
Q6. Atomic number of hydrogen (H) is:
The atomic number of hydrogen (H) is 1. This means hydrogen has 1 proton in its nucleus and 1 electron in a neutral atom. Hydrogen is the simplest and lightest element.
Q7. The mass of a proton is taken as:
The mass of a proton is taken as 1 u (unified atomic mass unit). Both protons and neutrons have approximately the same mass (about 1 u). The electron has negligible mass (about 1/2000 u).
Q8. The fractional atomic mass (like 35.5 u for chlorine) represents:
The fractional atomic mass (like 35.5 u for chlorine) represents the weighted average of the masses of all naturally occurring isotopes of that element. Chlorine has two main isotopes: chlorine-35 and chlorine-37, and their average is 35.5 u.
Q9. Chlorine’s average atomic mass is:
Chlorine’s average atomic mass is 35.5 u. This is the weighted average of its two main isotopes: chlorine-35 (about 75% abundance) and chlorine-37 (about 25% abundance). This is why chlorine has a fractional atomic mass.
Q10. Isobars differ in:
Isobars differ in atomic number (number of protons). They have the same mass number but different atomic numbers. This means they have different numbers of protons and different numbers of neutrons, but the total number of nucleons (protons + neutrons) is the same.
Q11. Isotopes are atoms of:
Isotopes are atoms of the same element (same atomic number) but with different mass numbers because they have different numbers of neutrons. For example, hydrogen has isotopes: protium (¹H), deuterium (²H), and tritium (³H).
Q12. The mass of an atom of an element with no isotopes equals:
The mass of an atom of an element with no isotopes equals the sum of protons and neutrons. Since electrons have negligible mass, the atomic mass is essentially the mass of the nucleus, which contains protons and neutrons.
Q13. The average atomic mass of an element is calculated using:
The average atomic mass of an element is calculated using the masses of its isotopes and their relative abundance in nature. This is why chlorine has an average atomic mass of 35.5 u, not a whole number.
Q14. Calcium (Z=20) and Argon (Z=18) have same mass number 40. They are:
Calcium (Z=20) and Argon (Z=18) have the same mass number (40) but different atomic numbers. This makes them isobars. Calcium-40 and argon-40 have different numbers of protons and neutrons but the same total number of nucleons.
Q15. Isotopes have:
Isotopes have the same number of protons (same atomic number) but different numbers of neutrons. This is why they are atoms of the same element. They have the same electronic configuration and therefore similar chemical properties.
Q16. Tritium (T) has number of neutrons:
Tritium (T) has 2 neutrons. It is an isotope of hydrogen with atomic number 1 and mass number 3. Since it has 1 proton, the number of neutrons = mass number – atomic number = 3 – 1 = 2. Tritium is a radioactive isotope of hydrogen.
Q17. Atomic number determines:
The atomic number determines the type of element. The atomic number is the number of protons in the nucleus, which defines the element. Elements with different atomic numbers are different elements. The chemical properties of an element are also determined by the atomic number (which determines the number of electrons).
Q18. Isobars are atoms of:
Isobars are atoms of different elements (different atomic numbers) that have the same mass number. They have the same total number of nucleons (protons + neutrons) but different numbers of protons and neutrons.
Q19. The mass of an atom of a natural element is:
The mass of an atom of a natural element is the average of all naturally occurring isotopes. Since most elements occur as mixtures of isotopes, the atomic mass listed in the periodic table is a weighted average of the masses of these isotopes.
Q20. Mass number of an atom equals:
The mass number of an atom equals the total number of nucleons (protons + neutrons) in the nucleus. It is often denoted by A. For example, carbon-12 has 6 protons and 6 neutrons, so its mass number is 12.
Q21. Atomic number of an element equals:
The atomic number of an element equals the number of protons in the nucleus. It is often denoted by Z. In a neutral atom, the number of electrons is also equal to the atomic number, but the defining characteristic of an element is the number of protons.
Q22. Neutrons carry:
Neutrons carry no charge (they are electrically neutral). They were discovered by James Chadwick in 1932 and are found in the nucleus of atoms. Their neutrality helps prevent protons (which repel each other) from flying apart due to electrostatic repulsion.
Q23. If an element has no isotopes, the mass of its atom equals:
If an element has no isotopes, the mass of its atom equals the sum of protons and neutrons. Electrons have negligible mass. For example, a single atom of fluorine-19 has 9 protons and 10 neutrons, giving a mass of 19 u.
Q24. An isotope of uranium is used as:
An isotope of uranium (U-235) is used as fuel in nuclear reactors. It undergoes nuclear fission, releasing a large amount of energy. This energy is used to generate electricity. Uranium-235 is the most common isotope used for this purpose.
Q25. The ratio of chlorine isotopes 35:37 is used to calculate:
The ratio of chlorine isotopes 35:37 is used to calculate the average atomic mass. Since chlorine occurs as a mixture of Cl-35 and Cl-37 in a certain ratio, the average atomic mass of chlorine (35.5 u) is calculated from this ratio.
Q26. Number of nucleons in an atom is:
The number of nucleons (protons + neutrons) in an atom is the mass number. It is represented by A. The mass number is the total count of particles in the nucleus.
Q27. Isotopes differ in:
Isotopes differ in the number of neutrons. They have the same atomic number (same number of protons) and the same number of electrons, but different numbers of neutrons. This is what gives them different mass numbers.
Q28. Isotopes are atoms of the same element with:
Isotopes are atoms of the same element with different mass numbers. They have the same atomic number but different numbers of neutrons, leading to different mass numbers. For example, carbon-12 and carbon-14 are isotopes.
Q29. Percentage of isotopic forms is needed to calculate:
The percentage of isotopic forms is needed to calculate the average atomic mass of an element. The average atomic mass is the weighted average of the masses of all naturally occurring isotopes, considering their relative abundances.
Q30. Protons carry:
Protons carry a positive charge (+1). They are found in the nucleus of atoms. The positive charge of protons is balanced by the negative charge of electrons in a neutral atom, making the atom electrically neutral.
Q31. Hydrogen, Deuterium, Tritium are examples of:
Hydrogen, deuterium, and tritium are examples of isotopes. They all have atomic number 1 (one proton) but different mass numbers (1, 2, and 3) due to different numbers of neutrons (0, 1, and 2 respectively). They are isotopes of hydrogen.
Q32. Elements are defined by:
Elements are defined by the number of protons in the nucleus. This is the atomic number. Every element has a unique atomic number, which distinguishes it from other elements. For example, any atom with 6 protons is carbon, regardless of the number of neutrons.
Q33. Isotopes have chemical properties:
Isotopes have the same chemical properties. This is because chemical properties depend on the number of valence electrons, which is the same for isotopes of an element. They differ only in physical properties like mass and density.
Q34. Physical properties of isotopes are:
Physical properties of isotopes are different. Because isotopes have different masses, they have different physical properties such as density, melting point, boiling point, and rates of diffusion. However, their chemical properties are the same.
Q35. Average atomic mass of an element is:
The average atomic mass of an element is the weighted mean of the masses of its isotopes, taking into account the relative abundance of each isotope in nature. This is why many elements have fractional atomic masses.
Q36. Chlorine occurs naturally in two isotopic forms with masses:
Chlorine occurs naturally in two isotopic forms with masses 35 u and 37 u. The most common isotope is chlorine-35 (about 75%), and the other is chlorine-37 (about 25%). This gives chlorine an average atomic mass of 35.5 u.
Q37. The fractional mass of 35.5 u of chlorine indicates:
The fractional mass of 35.5 u of chlorine indicates the average mass of a sample containing isotopes. It does not mean that every chlorine atom has a mass of 35.5 u; rather, it is the weighted average of Cl-35 and Cl-37 atoms.
Q38. The ratio of chlorine isotopes 35 u : 37 u is:
The ratio of chlorine isotopes 35 u : 37 u is approximately 3:1. That is, chlorine-35 is about three times more abundant than chlorine-37. This ratio (about 75% Cl-35 and 25% Cl-37) gives chlorine its average atomic mass of 35.5 u.
Q39. Mass number =
Mass number = atomic number + neutron number. It is the total number of protons and neutrons (nucleons) in the nucleus. For example, sodium-23 has atomic number 11 and 12 neutrons, so mass number = 11 + 12 = 23.
Q40. Sub-atomic particles of an atom are:
The sub-atomic particles of an atom are electrons, protons, and neutrons. Protons and neutrons are in the nucleus, while electrons orbit around the nucleus. These three particles make up all atoms.
Q41. Iodine isotope is used in:
Iodine-131 is an isotope of iodine used in the treatment of goitre and thyroid disorders. It is also used in the diagnosis and treatment of certain thyroid cancers. Radioactive iodine is used in nuclear medicine.
Q42. The average atomic mass of chlorine is:
The average atomic mass of chlorine is 35.5 u. This is because chlorine is a mixture of two isotopes: chlorine-35 (about 75%) and chlorine-37 (about 25%). The weighted average gives 35.5 u.
Q43. Applications of isotopes include:
Applications of isotopes include fuel (uranium in nuclear reactors), medical (cobalt-60 for cancer treatment, iodine-131 for thyroid treatment), and chemical (as tracers in chemical reactions). They have a wide range of uses in many fields.
Q44. An isotope of iodine is used in the treatment of:
An isotope of iodine (iodine-131) is used in the treatment of goitre (enlarged thyroid gland). It is also used to treat thyroid cancer. The iodine is absorbed by the thyroid gland and destroys abnormal cells.
Q45. The mass of a neutron is taken as:
The mass of a neutron is taken as 1 u (approximately). Neutrons and protons have nearly the same mass. The neutron is slightly heavier than the proton, but for most calculations, they are both considered to have a mass of 1 u.
Q46. Isotopes have physical properties:
Isotopes have different physical properties because they have different masses. These differences affect properties such as density, melting point, boiling point, and rate of diffusion. However, their chemical properties are the same.
Q47. Cobalt isotope is used in:
Cobalt-60 is used in treating cancer through radiotherapy. It emits gamma rays that can destroy cancer cells. It is one of the most commonly used radioisotopes for cancer treatment.
Q48. Electrons carry:
Electrons carry a negative charge (-1). They are found in the space around the nucleus and are responsible for chemical bonding. The negative charge of electrons balances the positive charge of protons in a neutral atom.
Q49. Isobars have:
Isobars have the same mass number but different atomic numbers. This means they have the same total number of nucleons (protons + neutrons) but different numbers of protons and neutrons. They are atoms of different elements.
Q50. Uranium isotope is used in:
Uranium-235 is used as fuel in nuclear reactors. It undergoes fission, releasing enormous amounts of energy used to generate electricity. It is also used in nuclear weapons. Other uranium isotopes are used in different applications, but the main use is in nuclear reactors.