$A$ compound contains $69.5\%$ oxygen and $30.5\%$ nitrogen and its molecular weight is $92$. The formula of that compound is

$A$ man running round a race-course notes that the sum of the distances of two flag-posts from him is always $10 \ m$ and the distance between the flag-posts is $8 \ m$. The area of the path he encloses in square metres is (in $\pi$)

The relative reactivities of acyl compounds towards nucleophilic substitution are in the order of

The angle between the lines whose direction cosines are given by the equations $l^2+m^2-n^2=0$ and $l+m+n=0$ is

Which one of the following is formed apart from sodium chloride when chlorine reacts with hot concentrated sodium hydroxide?

Which era is known as the age of birds and mammals?