Question

A positron is emitted by radioactive nucleus of proton number $90$. The product nucleus will have proton number :

• A. $91$
• B. $90$
• C. $89$
• D. $88$

Answer 1

Answer: (C)

$89$

The given nuclear reaction is-

${}_{90}X{\to }_{+1}e$ $+$ ${}_{z}Y$

Using law of conservation of atomic (or proton) number:

$90=1+Z$

$⟹$ $Z=89$

Thus the product nucleus will have proton number $89$.