The correct option in this case is A: Both A and R are true, and R is the correct explanation of A.

The assertion states that the rate of growth of India`s exports has shown an appreciable increase after 1991, which is true. The liberalization of the Indian economy, initiated in 1991, led to significant economic reforms, including trade reforms. These reforms aimed at reducing trade barriers, promoting exports, and integrating India into the global economy. As a result, India experienced a boost in its export growth rate, with exports increasing at a faster pace post-1991.

The reason provided is that the Government of India has resorted to devaluation, which is also true and provides a valid explanation for the increased export growth rate. Devaluation refers to a deliberate reduction in the value of a country`s currency relative to other currencies. It can make the country`s exports relatively cheaper and more competitive in the global market, leading to an increase in export volumes. Devaluation can be one of the measures employed by the government to enhance export growth.

Therefore, in this case, both the assertion and the reason are true, and the reason provided is a correct explanation for the assertion.