The correct formula of calcium hydroxide is -

A solution of a substance 'X' is used for whitewashing.

(a) Name the substance 'X' and write its formula.

(b) Write the reaction of the substance with water.

Find the empirical formula and the molecular formula of an organic compound from the data given below:

$\mathrm{C} = 75.92\%, \mathrm{H} = 6.32\% \mathrm{and} \mathrm{N} = 17.76\%$

The vapour density of the compound is $39.5$.  $[\mathrm{C} = 12, \mathrm{H} = 1, \mathrm{N} = 14]$

Which elements are present in the following?

${\mathrm{CO}}_2$.