[nicolodn]

A Student uses another calorimeter with a heat capacity of 133.2 J/°C. S/he fills the calorimeter with 100.0 g of 25.00°C dilute HCl solution and adds 0.496 g Mg metal (24.3 g/mol). The final temperature of the apparatus comes to 41.37°C.
What is the enthalpy change for the reaction as written?

Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)

Take the specific heat capacity of the dilute acid solution as being equal to that of water, and neglect the heat capacity of the magnesium metal.

Hint:   the heat evolved by the Mg reaction is gained by the water and calorimeter

I keep getting the wrong answer.
I did q=m x C X T  + c x T

What am I doing wrong?

[Borek]

You probably should answer in kJ per mole, not just kJ.

That is - I am guessing what you did, as you have not presented any numbers.