$4^n=(2^2)^n=2^{2n}$, whose only prime factor is 2 (no factor of 5). A number ends in 0 only if it is divisible by 10 = 2x5, requiring both 2 and 5 as factors. Since $4^n$ has no factor of 5, it can never end in 0 — Assertion is TRUE. By the Fundamental Theorem of Arithmetic, the prime factorisation of $4^n$ is unique (Reason is TRUE), and this uniqueness is exactly why we can be sure $4^n$ has no factor of 5, correctly explaining the Assertion.