Give scientific reason:

When the gas formed on heating limestone is passed through freshly prepared lime water, the lime water turns milky.

Give scientific reason:

It takes time for pieces of Shahabad tile to disappear in $\mathrm{HCl}$, but its powder disappears rapidly.

Give scientific reason:

While preparing dilute sulphuric acid from concentrated sulphuric acid in the laboratory, the concentrated sulphuric acid is added slowly to water with constant stirring.

Give scientific reason:

It is recommended to use air tight container for storing oil for long time.

Observe the following picture and write-down the chemical reaction with explanation.

Identify from the following reaction, the reactants that undergo oxidation and reduction.

$\mathrm{Fe} + \mathrm{S} \to \mathrm{FeS}$

Identify from the following reaction, the reactants that undergo oxidation and reduction.

$2{\mathrm{Ag}}_2\mathrm{O} \to 4 \mathrm{Ag} + {\mathrm{O}}_2$

Identify from the following reaction, the reactants that undergo oxidation and reduction.

$2\mathrm{Mg} + {\mathrm{O}}_2\to 2\mathrm{MgO}$

Identify from the following reaction, the reactants that undergo oxidation and reduction.

$\mathrm{NiO} + {\mathrm{H}}_2\to \mathrm{Ni} + {\mathrm{H}}_2\mathrm{O}$