Final answer:
A specific overproduction of aldosterone, which regulates salt balance, can be best explained by a tumor in the adrenal cortex.
Step-by-step explanation:
The client's specific overproduction of aldosterone, a hormone that regulates salt balance in the body, can be best explained by a tumor in the adrenal cortex. The adrenal cortex is responsible for producing mineralocorticoids, including aldosterone, which plays a key role in sodium reabsorption. Therefore, a tumor in the adrenal cortex can lead to excessive production of aldosterone and disruption in salt balance.