Which among the give nmolecules can exhibit tautomerism?

The correct structure of the product A formed in the reaction:

Consider the reaction :

CH₃CH₂CH₂Br + NaCN  → CH₃CH₂CH₂CN + NaBr

This reaction will be the fastest in :

A given nitrogen-containing aromatic compound A reacts with Sn/HCl, followed by HNO₂ to give an unstable compound B. B, on treatment with phenol, forms a beautiful coloured compound C with the molecular formula C₁₂H₁₀N₂O. The structure of compound A is :

Iron and manganese are removed in water by the process of:

Consider the following four particles :

1. Alpha particle
2. Proton
3. Electron
4. Neutron

Which of the following is the correct sequence in which their rest-masses increase?