Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Ionisation enthalpies of early actinoids are lower than for early lanthanoids. Reason (R) : Electrons are entering $5 f$ orbitals in actinoids which experience greater shielding from nuclear charge. In the light of the above statements, choose the correct answer from the options given below:

• Correct answer
  A

  Both $(\mathbf{A})$ and $(\mathbf{R})$ are true and $(\mathbf{R})$ is the correct explanation of $(\mathbf{A})$.
• B

  Both $(\mathbf{A})$ and $(\mathbf{R})$ are true but $(\mathbf{R})$ is not the correct explanation of $(\mathbf{A})$.
• C

  (A) is true but (R) is false.
• D

  (A) is false but $(\mathbf{R})$ is true.

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