**Step 1 — Write out the first few powers of 5.**
$$5^1 = 5,\quad 5^2 = 25,\quad 5^3 = 125,\quad 5^4 = 625$$

**Step 2 — Observe the unit digit.**
The unit digit is always $5$.

**Step 3 — Reason algebraically.**
$5^n = 5 \times 5^{\,n-1}$. A number ending in $5$ multiplied by $5$ always ends in $5$.

Also note: $5^n$ can never end in $0$, because $5^n$ has no factor $2$ (a number ends in $0$ only if it is divisible by $10 = 2 \times 5$).

**Answer : (B) 5**