In the Lassaigne’s test for nitrogen in an organic compound, the Prussian blue colour is obtained due to the formation of-

$1. {\mathrm{Na}}_4\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$
$2. {\mathrm{Fe}}_4[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6{]}_3$
$3. {\mathrm{Fe}}_2\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$
$4. {\mathrm{Fe}}_3[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6{]}_4$

Lassaigne's test can detect:

1. Nitrogen, Sulphur, Halogens

2. Nitrogen, Cyanides, Sulphur

3. Sodium, Sulphur, Halogens, Phosphorus

4. Nitrogen, Sulphur, Halogens, Phosphorus

Nitric acid is added to sodium extract before adding silver nitrate for testing halogens because:

1. Nitric acid reduces sulphide

2. Nitric acid decomposes NaCN and Na₂S

3. Nitric acid oxidises the organic compound

4. Nitric acid acts as a dehydrating agent

A mixture of calcium sulphate and camphor can be separated by- 
1. Filtration
2. Evaporation
3. Sublimation
4. Chromatography

A gas among the following that can be absorbed by potassium hydroxide is -