NEET Chemistry: Nuclear Chemistry questions with solutions

Q1. A radioactive atom ' \( X^{\prime} \) emits a \( \beta- \) particle to produce an atom ' \( Y \) ' which then emits an \( \alpha \) -particle to given an \( \operatorname{atom}^{\prime} Z^{\prime}: \) (1) The atomic number of ' \( X^{\prime} \) is less than that of \( ^{\prime} Z^{\prime} \) (2) The atomic number of ' \( Y \) ' is less than that of \( ^{\prime} Z^{\prime} \) (3) The mass number of ' \( X^{\prime} \) is same as that of ' \( Y \)

1. 1,2 and 3 are correct
2. 1 and 2 are correct
3. 2 and 3 are correct
4. 3 is correct

Answer: 3 is correct

A beta-minus decay increases atomic number by 1 while leaving mass number unchanged, so X and Y have the same mass number. Then an alpha decay decreases atomic number by 2 and mass number by 4, making Z have atomic number one less than X and mass number four less than Y. Thus only statement 3 is true.

Q2. Heavy water \( \left(D_{2} O\right) \) is used in Atomic Reactors as -

1. Coolant
2. Controller
3. shield
4. Moderator

Answer: Moderator

Heavy water is used as a moderator because it reduces the speed of fast neutrons to thermal energies while absorbing relatively few neutrons. This makes the chain reaction more likely to continue in the reactor core.

Q3. ⁹²U²³⁵ nucleus absorbs a neutron and disintegrates into ⁵⁴Xe¹³⁹, ³⁸Sr⁹⁴ and x. So what will be the product x?

1. 3-neutrons
2. 2-neutrons
3. α-particle
4. β-particle

Answer: 3-neutrons

The total mass number and atomic number must be conserved. The sum of mass numbers of ⁵⁴Xe¹³⁹ (139), ³⁸Sr⁹⁴ (94), and x must equal 236 (235 + 1 neutron). Similarly, the sum of atomic numbers must equal 92. This conservation confirms x is 3 neutrons.