Final answer:
The correct cause of weight loss in older cats among the options provided is hyperthyroidism, leading to an increased metabolic rate, resulting in weight loss and other symptoms like sweating and a raised heart rate.
Step-by-step explanation:
Common causes of weight loss in older cats can include several health issues, one of which is hyperthyroidism. Unlike hypothyroidism, which is characterized by a decreased metabolic rate leading to weight gain and reduced mental activity, hyperthyroidism is the overproduction of thyroid hormones. This condition can lead to an increased metabolic rate which may cause symptoms such as weight loss, excessive heat production, profuse sweating, and an elevated heart rate. Graves' disease is a well-known form of hyperthyroidism.
Therefore, the correct answer to the question is c) Hyperthyroidism, which is known to result in weight loss, as well as other symptoms like profuse sweating and increased heart rate in cats.