In the equation: X →
226
88
Ra + He
The symbol Xrepresents
A)
222
Th
86
222
B)
Rn
86
230 Th
C)
90
D)
230
90
Rn

²³⁰₉₀Th

Explanation:

X  →  ²²⁶₈₈Ra  +   ⁴₂He

The given equation shows the alpha emission. When He particle emit the original atom convert into the atom having mass number less than 4  and atomic number less than 2 as compared to parent atom the starting atom.  It means the parent atom is  ²³⁰₉₀Th.

Alpha radiations are emitted as a result of radioactive decay. The atom emit the alpha particles consist of two proton and two neutrons. Which is also called helium nuclei. When atom undergoes the alpha emission the original atom convert into the atom having mass number less than 4  and atomic number less than 2 as compared to parent atom the starting atom.

Alpha radiations can travel in a short distance.

These radiations can not penetrate into the skin or clothes.

These radiations can be harmful for the human if these are inhaled.

These radiations can be stopped by a piece of paper.

₉₂U²³⁸   →   ₉₀Th²³⁴  + ₂He⁴  + energy