Assertion: The unit of rate constant is (mole)^1-n (litre)^n-1 time^-1 .

Reason: The unit of rate constant for first order reaction is s^-1.

Assertion and Reason both are correct statements and reason is the correct explanation for assertion.

The unit of rate constant is (mole)^1-n (litre)^n-1 time^-1 , n = order of reaction

For first order reaction, n = 1

(mole)^1-1 (litre)^1-1 s^-1 = (mole)⁰ (litre)⁰ s^-1 = s^-1