What is the percentage of formaldehyde in formalin (in $\%$)?

An organic compound $A$ reacts with methyl magnesium iodide to form an addition product,which on hydrolysis gives compound $B$. Compound $B$ gives a blue color in the Victor Meyer test. What are compounds $A$ and $B$ respectively?

The relation between $K_1$ and $K_2$ for the given equilibrium reactions is:

Given below are two statements:
Statement $I:$ The boiling points of aldehydes and ketones are higher than hydrocarbons of comparable molecular masses because of weak molecular association in aldehydes and ketones due to dipole-dipole interactions.
Statement $II:$ The boiling points of aldehydes and ketones are lower than the alcohols of similar molecular masses due to the absence of $H$-bonding.
In the light of the above statements,choose the most appropriate answer from the options given below:

In which of the following reactions,two products will be formed other than triphenylphosphine oxide $(Ph_3PO)$?

For the sequence of reactions $A$ $\xrightarrow{C_2H_5MgI} B$ $\xrightarrow{H_2O / H^{+}} \text{tert-pentyl alcohol}$. The compound $A$ in the sequence is