What may be the reason for geometrical isomerism?

Restricted rotation about a double bond.

Isomerism exhibited by tartaric acid

Optical isomerism

Isomerism exhibited by maleic & fumaric acid

Geometrical isomerism

Most volatile hydrogen halides

We all are familiar with the different types of hydrogen halides. Do you know which are they? Remember that the different types of hydrogen halides include HF, HBr,HCl & HI. Do you know among these halides which is the most volatile?
Note that the most volatile hydrogen halide is HCl.

What is ammonal?

Remember that ammonal is a mixture of aluminium powder & ammonium nitrate.

Do you know the reason why sodium nitrate is not used in gun powder?

This is becuase it is hygroscopic.

What happens when sodium burns in excess of air?.

Sodium peroxide is formed.