What is the major product of the nitration of benzoic acid?

Which one of the following will undergo decarboxylation on heating?

What is the correct acidic strength order of the following compounds?

$A$ colourless water-soluble organic liquid decomposes sodium carbonate and liberates carbon dioxide. It produces a black precipitate with Tollen's reagent. The liquid is

Arrange the following in decreasing order of their acidic strength and give reason for your answer: $CH_{3}CH_{2}OH$,$CH_{3}COOH$,$ClCH_{2}COOH$,$FCH_{2}COOH$,$C_{6}H_{5}CH_{2}COOH$.

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?