Write true or false for the following statement:
Mixing an acid or base with water results in an increase in the concentration of ions $(H_{3}O^{+} / OH^{-})$ per unit volume.

Which of the following solutions is most basic?

When $Zn$ metal is treated with a dilute solution of a strong acid,a gas is evolved,which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.

In the following schematic diagram for the preparation of hydrogen gas as shown in the Figure,what would happen if the following changes are made?
$(a)$ In place of zinc granules,the same amount of zinc dust is taken in the test tube.
$(b)$ Instead of dilute sulphuric acid,dilute hydrochloric acid is taken.
$(c)$ In place of zinc,copper turnings are taken.
$(d)$ Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.

Sodium hydrogencarbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved?
$(i)$ It turns lime water milky
$(ii)$ It extinguishes a burning splinter
$(iii)$ It dissolves in a solution of sodium hydroxide
$(iv)$ It has a pungent odour

Which of the following metals reacts with sodium hydroxide to produce a salt and $H_2$ gas?