The formula for molarity is:
M = n/V
or
M = mol/L
All you need to do is substitute the values you are given.
M = 4.25
L = 2.5
n = ?
4.25 = n/2.5
Multiply both sides by 2.5 to isolate n.
10.625 = n
There are 10.6 moles of H2So4 in the aqueous solution.