Reducing property of formic acid is due to the presence of:

Some pairs of acids are given below. Select the pair in which the second acid is stronger than the first.

An optically active compound $X$ has molecular formula $C_4H_8O_3$. It evolves $CO_2$ with $NaHCO_3$. $X$ reacts with $LiAlH_4$ to give an achiral compound. $X$ is

The decreasing order of nucleophilicity among the following nucleophiles is:
$(I)$ $CH_3-COO^{-}$
$(II)$ $CH_3O^{-}$
$(III)$ $C_6H_5O^{-}$
$(IV)$ $CH_3-SO_3^-$

Which of the following acids has the lowest $pK_a$ value?

Oxalic acid reacts with concentrated $H_2SO_4$ to give a mixture of two gases. When this mixture is passed through caustic potash,one of the gases is absorbed. What is the product formed by the absorbed gas with caustic potash?