Question

A certain nucleus X has a mass number 15 and atomic number 7. Find the number of neutrons. The nucleus X losses one α-particle and Express the change and write the symbol of the new nucleus.

Answer 1

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

Atomic number = No. of protons

∴ No. of neutrons = Mass number - Atomic number 

= 15 - 7 = 8

Element X can be written as \[\ce{_7^15X}\].

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

\[\ce{_7^15X -> _5^11Z + _2^4He}\]