Question

Which of the following represents positron emission? Select one: a. 3015P ---> 3014Si + ___ b. 23892U ---> 23490Th + ___ c. 147N + 42He --->178O + ___ d. 23490Th ---> 23491Pa + ___

Answer 1

The simple trick which one can consider in such problem where it is asked for positron emission is :
When the atomic number goes DOWN by one and mass number remains unchanged, then a positron is emitted.

a.  $P^{30}_{15} ----\ \textgreater \ Si^{30}_{14} + e^{0}_{1}^+$

Here the atomic number decreases by one.

Similarly, options b and d are eliminated.

Option c is also not the answer.
For c, Count the atomic number on left side and compare it with right side. You will see it is 9 on left and 8 on right. Atomic no. did go down by 1. But the atomic mass is changed as well.