Question

zinc can produce hydrogen on reacting with acids but copper cannot.Explain

Answer 1

because copper is less reactive than zinc

Answer 2

If you see the reactivity series of metals, then you may observe that Zn(zinc) is more reactive than H(hydrogen). So,Zn will displace H in any reaction of Zn with acids.
On the contrary, Copper is less reactive than hydrogen, so it would not displace hydrogen.