On heating an aliphatic primary amine with chloroform and ethanolic potassium hydroxide, the organic compound formed is:

The most suitable reagent for the conversion of R - CH₂ - OH $$\to$$ R - CHO is:

In the reaction,

the product C is:

In S_N2 reactions, the correct order of reactivity for the following compounds:
CH₃Cl, CH₃CH ₂Cl, (CH₃)₂CHCl and (CH₃)₃CCl is: