The correct answer is (C) because the assertion (a) is true, but the reason (r) is false.
People suffering from eating disorders like anorexia nervosa and bulimia nervosa are indeed preoccupied with food, dieting, and their body weight, often exhibiting an intense fear of gaining weight and distorted body image.
However, eating disorders are more commonly diagnosed in adolescents and young adults rather than in older adults. While adults can also suffer from these disorders, the prevalence is higher among teenagers and young adults, making the reason statement inaccurate.