Which among the following compounds is a weakest base?

Identify lowest positive charge developed (indicated by $$\partial, \partial_1, \partial_2, \partial_3$$) due to inductive effect in following compounds.

$$\mathrm{C{H_3} - \mathop {C{H_2}}\limits^{{\delta _3}} \to \mathop {C{H_2}}\limits^{{\delta _2}} \to \mathop {C{H_2}}\limits^{{\delta _1}} \to \mathop {Cl}\limits^{{\delta _{}}}}$$

Which among following functional groups exhibits $$-\mathrm{R}$$ effect?

Which from following statements is true for tetrahydrofuran?