Assertion (A): For a number to end with the digit zero, its prime factorisation must contain both 2 and 5.Prime factorisation of $4^n = (2^2)^n = 2^{2n}$The only prime factor of $4^n$ is 2. Since 5 is not a prime factor, $4^n$ can never end with the digit zero for any natural number n.So, Assertion is true.Reason (R):The Fundamental Theorem of Arithmetic states that the prime factorisation of every composite number is unique, apart from the order of its factors.So, Reason is true.However, the uniqueness of prime factorisation (Reason) is the underlying principle used to confirm that no other prime (like 5) can exist in the factorisation of $4^n$.Thus, Reason is the correct explanation for Assertion.