The products A and B for the given reaction 

​are, respectively

​

Correct option is C

In inner sphere electron transfer reactions, the oxidant and reductant share a ligand in their coordination sphere to form a bridged complex, the electron is then transferred through the bridging ligand. An important reaction involving electron transfer by inner sphere mechanism is discussed below:

In this reaction Co³⁺is reduced by Cr²⁺and the bridging ligand Cl^-is transferred from coordination sphere of cobalt to that of chromium.

i. $$[\text{Co(NH}_3\text{)}_5\text{Cl}]^{2+}$$is kinetically inert and Cl^-is the bridging ligand.

ii. Electron transfer takes place from $$e_g (\sigma^*) \, \text{of} \, [\text{Cr(H}_2\text{O)}_6]^{2+} \, \text{to} \, e_g (\sigma^*) \, \text{of} \, [\text{Co(NH}_3\text{)}_5\text{Cl}]^{2+}$$

Thus, electron transfer by inner sphere mechanism is fast (rate constant (k)=6×10⁵Lmol^-1s^-1). The various steps of the mechanism of the reaction are shown below:

i. Chlorine atom of inert $$[\text{Co(NH}_3\text{)}_5\text{Cl}]^{2+}$$complex while remaining firmly attached to Co(III) replaces a water molecule from the labile $$[\text{Cr(H}_2\text{O)}_6]^{2+}$$to form a bridged intermediate.

ii. Electron transfer takes place from Cr(II) to Co(III) through Cl bridge in a manner as electron flows between two electrodes through salt bridge. This step is the rate determining step. After transfer of electron from Cr²⁺ to Co³⁺, Co³⁺ is converted to Co²⁺ and the complex becomes high spin and labile. On the other hand, Cr²⁺ is converted to Cr³⁺ and the complex becomes inert.

iii. Since Co²⁺is now labile and Cr³⁺is inert, so the bridged complex intermediate dissociates in such a way that chlorine atom remains attached with chromium.

iv. In the last step, the five coordinate [Co(NH₃)₅]²⁺species picks up water molecule to form $$[\text{Co(NH}_3\text{)}_5(\text{H}_2\text{O})]^{2+}$$complex ion and this complex ion is hydrolyzed rapidly to give [Co(H₂O)₆]²⁺ion.

​An evidence to support the inner sphere mechanism is that if the reaction is carried out in solution containing free isotopic chlorine (e.g.³⁶Cl^-), none of these labeled ions are found in the products. Conversely, if Cl^- ion in [Co(NH₃)₅Cl]²⁺ is isotopically labeled with ³⁶Cl, the labeled ³⁶Cl is always transferred to Cr (III) coordination sphere. The reaction is first order with respect to oxidant and first order with respect to reductant i.e., overall reaction is of second order.

$$\text{Rate} = k \, [\text{oxidant}] [\text{reductant}] \\= k \, [\text{Co(NH}_3\text{)}_5\text{Cl}]^{2+} [\text{Cr(H}_2\text{O)}_6]^{2+}$$

k is the second order rate constant. 

The general reaction is given below: