Assertion (A): For a weak electrolyte, the degree of dissociation at concentration $c$ can be taken as $\alpha ={\Lambda }_m/{\Lambda }_m^{\circ }$. Reason (R): It is assumed that the mobilities of the ions at concentration $c$ are the same as at infinite dilution, so that ${\Lambda }_m$ is proportional only to the fraction of molecules dissociated. Choose the correct option.

1. ABoth (A) and (R) are true and (R) is the correct explanation of (A)
2. BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
3. C(A) is true but (R) is false
4. D(A) is false but (R) is true