A number is divisible by 6 only if it is divisible by both 2 and 3.

Divisibility by 2: the number must be even (last digit 0, 2, 4, 6 or 8).

Divisibility by 3: the sum of the digits must be a multiple of 3.

Check 5,47,821: last digit is 1 (odd), so it fails the test for 2 and is not divisible by 6.

Check 7,53,216: last digit is 6 (even), so it is divisible by 2. Digit sum \(7+5+3+2+1+6 = 24\), and \(24 \div 3 = 8\), so it is divisible by 3 as well.

Since 7,53,216 is divisible by both 2 and 3, it is divisible by 6. A quick check: \(753216 \div 6 = 125536\), an exact whole number.

Check 8,91,452: digit sum \(8+9+1+4+5+2 = 29\), not a multiple of 3, so it fails.

Check 6,42,538: last digit 8 is even, but digit sum \(6+4+2+5+3+8 = 28\) is not a multiple of 3, so it fails.

Hence, the number completely divisible by 6 is 7,53,216.