Assertion: At rest, radium is decayed into Radon and an $\alpha$-particle. They both moves back to back of each other.Reason : Splitting of radioactive particle is based on conservation of linear momentum.

• Correct answer
  A

  If both assertion and reason are true and reason is the correct explanation of assertion.
• B

  If both assertion and reason are true but reason is not the correct explanation of assertion.
• C

  If assertion is true but reason is false.
• D

  If both assertion and reason are false.

Hence, the correct answer is option: 'A'.