Question

When dilute hydrochloric acid is added to zinc pieces taken in a test tube

No change takes place
The colour of the solution becomes yellow
A pungent smelling gas gets liberated
Small bubbles of hydrogen gas appear on the surface of zinc pieces

Answer 1

when a metal react with acid it evolves hydrogen therefore small bubbles of hydrogen appear on the zinc pieces

Answer 2

Answer: Small bubbles of hydrogen gas appear on the surface of zinc pieces

Explanation: $Zn+2HCl(dil)\rightarrow ZnCl_2+H_2$

This is a single displacement reaction. Zinc being more reactive than hydrogen displaces hydrogen from its solution and forms zinc chloride which is white in color and liberates hydrogen gas which is a odorless gas.

Here zinc gets oxidized to $Zn^{2+}$ and $H^+$ in $HCl$ gets reduced to form hydrogen gas.