We know when H2SO4 REACTS WITH Cu then it gives a nascent atom of oxygen which oxidizes Cu and makes CuO.BUT WHEN HCL REACTS WITH Cu then why it can't give nascent chlorine, 2[CL] WHICH WOULD OXIDIZE THE Cu AND MAKE CuO.

SO WHY H2S04 CAN DO BUT HCL CAN'T DO THAT ?

Hint: Do the math.

Hint: 1 + 1 = 2

Why can it never equal 3?

This is because copper is below hydrogen in the reactivity series whereas magnesium is above hydrogen, causing a reaction