What is the number of magnesium atoms that equal a mass of 24.31 amu?

Atomic Mass of Magnesium  =  24.30 amu

As we know, 1 mole of Mg weights exactly 24.30 amu.
Also,
1 mole of Mg contains 6.022 × 10²³ Atoms.
So, If,

24.30 amu Mg contains  =  6.022 × 10²³ Mg Atoms
Then,
24.31 amu of Mg will contain  =  X Mg Atoms,

Solving for X,
                            X  =  (24.31 amu × 6.022 × 10²³ Atoms) ÷ 24.30

                            X  =  6.022 × 10²³ Mg Atoms

Result:
            24.31 amu of Mg equals 6.022 × 10²³ Mg Atoms.

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.

So3 that’s what i think