Given below are two statements : one is labelled as Assertion $\mathbf{A}$ and the other is labelled as Reason $\mathbf{R}$ :

Assertion A : The first ionisation enthalpy decreases across a period.

Reason $\mathbf{R}$ : The increasing nuclear charge outweighs the shielding across the period.

In the light of the above statements, choose the most appropriate from the options given below :

1. A $\mathbf{A}$ is false but $\mathbf{R}$ is true Correct answer
2. B Both $\mathbf{A}$ and $\mathbf{R}$ are true but $\mathbf{R}$ is NOT the correct explanation of $\mathbf{A}$
3. C Both $\mathbf{A}$ and $\mathbf{R}$ are true and $\mathbf{R}$ is the correct explanation of $\mathbf{A}$
4. D $\mathbf{A}$ is true but $\mathbf{R}$ is false