ORGANIC DOUBTS

In IV both reactions won't occur. No substitution or elimination reactions occur at the bridge head carbon, which is where Cl is situated here.
Due to the strained form in which it exists, the bridgehead carbon cannot be sp² hybridised or planar, which is what happens in the intermediates/transition states of subs/elmn.

1) mein I think HI(g) reaction won't occur..proton kaise dega if not in solvent? I am not sure, but I think so.

For HI(aq), products will be cyclohexyl alcohol and methyl iodide (S_N2 reaction)

in Ans 1 ..with HI(aq) the final product may be cyclohexyl iodide...since HI is a very good acid and alcohols are not generally stable in the presence of acids ..so the C-O bond will be cleaved and C-I bond may be formed..