At what $pH$ is rain water said to be acidic?

What happens when a solution of an acid is mixed with a solution of a base in a test tube?
$(i)$ The temperature of the solution increases
$(ii)$ The temperature of the solution decreases
$(iii)$ The temperature of the solution remains the same
$(iv)$ Salt formation takes place

Explain the action of dilute hydrochloric acid on the following with chemical equations:
$(a)$ Magnesium ribbon
$(b)$ Sodium hydroxide
$(c)$ Crushed egg shells

Which of the following gives the correct increasing order of acidic strength?

State what happens when zinc granules are heated with sodium hydroxide solution. Write the balanced equation for this reaction. Name the main product formed in this reaction.

Write the balanced chemical equations for the following reactions:
$(a)$ Chlorine is passed over dry slaked lime.
$(b)$ Sodium bicarbonate reacts with dilute hydrochloric acid.
$(c)$ Sodium bicarbonate is heated.