Question

metal X is treated with dilute acid Y then gas Z is evolved which burns readily by making a little explosion

Answer 1

The metal x is zinc and y is sulphuric acid then z is hydrogen gas.

Answer 2

Here X is a metal which react with dilute acid to release gas. Metals always release hydrogen gas with dilute acids.

Hence the Z gas must be hydrogen gas. Here X metal can zinc or iron as both releases hydrogen gas with dilute acid. The dilute acid Y is usually dilute HCl.  

Hence:

X  = Zn or Fe  

Y  = dil HCl

Z  = hydrogen gas that burns readily by making a little explosion.