A. A radioactive nucleus ‘A’ undergoes a series of decays as given below :
The mass number and atomic number of 
are 176 and 71 respectively. Determine the mass and atomic numbers of 
and A.
B. Write the basic nuclear processes underlying 
and 
decays.
A.
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We know that, when a nucleus undergoes
decay, its mass number decreases by 4 and atomic number decreases by 2, whereas for 
decay, the mass number remains same and the atomic number decreases by 1, and 
decay does not effect any of them. So, for the above decay we can write as,Hence,
For A4,
Mass number 172
Atomic number 69
For A,
Mass number 180
Atomic number 74.
B. For 
decay,
The mass number A does not change and the atomic number goes up by 1 u. In 
decay, a neutron decays into proton, electron and antineutrino, the corresponding nuclear equation is,
N → p + e-+ 
For 
decay,
The mass number A does not change and the atomic number reduces by 1 u. In 
decay, a proton decays into neutron, positron and neutrino, the corresponding nuclear equation is,
P → n + e+ + 
It is important to take a note, a free neutron can decay to proton, the decay of proton to neutron is possible only inside the nucleus, since proton has smaller mass than neutron.
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