The secondary structure of a protein refers to

In the following sequence of reactions,
CH₃CH₂OH $$\buildrel {P + {I_2}} \over \longrightarrow $$ A $$\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{ether}^{Mg}} $$ B $$\buildrel {HCHO} \over \longrightarrow $$ C $$\buildrel {{H_2}O} \over \longrightarrow $$ D
the compound ‘D’ is

Which of the following is the correct order of decreasing S_N2 reactivity?

Which one of the following is the strongest base in aqueous solution?