Assertion: Spearman's theory of intelligence suggests that there is a general factor, called the "g factor," which underlies all specific mental abilities.

Reasoning: According to Spearman's theory, the "g factor" represents the common variance shared by different cognitive tasks and reflects a person's overall intellectual ability.

Both the assertion and reasoning are true, and the reasoning is the correct explanation of the assertion.

The assertion states that Spearman's theory proposes the existence of a general factor, the "g factor," which is true. The reasoning provides the correct explanation by stating that the "g factor" represents the common variance among different cognitive tasks and reflects a person's overall intellectual ability. Therefore, both the assertion and reasoning are true, and the reasoning explains the assertion accurately.