The correct option is C 542
The largest number that can be formed from the digits 2, 4 and 5 is definitely a 3-digit number.
This number is got by placing :
1) the largest of these digits (5) in the first place (hundreds place),
2) the second largest number (4) in the second place (tens place) and
3) obviously, the smallest number in the units place.
Thus, the required number is 542.