Question

A certain nucleus X has a mass number of 16 and an atomic number of 7. Find the number of neutrons. The nucleus X emits one α-particle. Write the symbol of the new nucleus and express the change using a reaction.

Answer 1

Mass number = No. of protons + No. of neutrons

Atomic number = No. of protons

∴ No. of neutrons = Mass number − Atomic number 

= 16 − 7

= 9

Element X can be written as \[\ce{_7^16X}\].

After the loss of one α-particle, the mass number is decreased by 4 and the atomic number is decreased by 2. The element X changes to Y.

\[\ce{_7^16X -> _5^12Y + _2^4He}\]