Cassandra and Martin have been dating for some time. Cassandra recently gave Martin a framed print of a painting she had noticed him admiring on a previous trip to the museum. Martin now feels that he should buy Cassandra a bottle of her favorite perfume as a way of repaying her kindness. Which theory best explains Martin's response to Cassandra's gift?

Equity theory

Explanation:

Equity theory is a theory used in psychology that focuses on determining whether the distribution of resources is fair between two partners in a relationship (not necessarily romantic, but of cooperation). This theory states that if a relationship between two partners is too unequal, those within it are likely to be unhappy in a degree proportional to the inequality.