Among the following four aromatic compounds, which one will have the lowest melting point ?

In the following reaction :

Aldehyde + Alcohol   $$\buildrel {HCl} \over \longrightarrow $$  Acetal

Aldehyde			Alcohol
HCHO			tBuOH
CH3CHO			MeOH

The best combination is

If the sum of the deviations of 50 observations from 30 is 50, then the mean of these observations is :

A ratio of the 5th term from the beginning to the 5th term from the end in the binomial expansion of $${\left( {{2^{1/3}} + {1 \over {2{{\left( 3 \right)}^{1/3}}}}} \right)^{10}}$$ is :