The inert pair effect refers to the tendency of certain elements, particularly those in Groups 13 to 16 of the periodic table, to preferentially use their s-electrons in bonding rather than their p-electrons. This effect is primarily observed in elements with a high atomic number and is attributed to the increasing energy difference between the s and p orbitals as the atomic number increases.

Explanation:
The consequence of the inert pair effect can be observed in the oxidation states and reactivity of elements. Let's analyze each option to determine which one is a consequence of the inert pair effect.

(a) SnCl2 acts as a reducing agent:
This statement is not a consequence of the inert pair effect. SnCl2 is a reducing agent because it can donate electrons to other species and undergo oxidation itself. The inert pair effect does not directly influence the reducing properties of SnCl2.

(b) SnCl4 acts as an oxidizing agent:
This statement is a consequence of the inert pair effect. As the atomic number increases, the energy difference between the s and p orbitals becomes larger, making it more favorable for the element to utilize its s-electrons in bonding. In the case of SnCl4, tin is in the +4 oxidation state, indicating the use of all four of its valence p-electrons in bonding. This is a consequence of the inert pair effect.

(c) TlCl acts as an oxidizing agent:
This statement is not a consequence of the inert pair effect. TlCl is an ionic compound where thallium is in the +1 oxidation state. The inert pair effect is not directly related to the oxidizing properties of TlCl.

(d) PbO2 is an oxidant:
This statement is not a consequence of the inert pair effect. PbO2 is an oxidizing agent because it can accept electrons from other species and undergo reduction itself. The inert pair effect does not directly influence the oxidizing properties of PbO2.

Therefore, the correct answer is option (b) - SnCl4 acts as an oxidizing agent. This is a consequence of the inert pair effect, as the tin atom utilizes its s-electrons in bonding, resulting in a higher oxidation state of +4.