Which of the following are examples of disorders of thought form (rather than content)?

Correct option is B

Disorders of thought form affect the way thoughts are expressed (tangentiality, circumstantiality, derailment). Disorders of thought content are delusions.
Explanation of options: (a) ✘ Delusions are abnormal thought content. (b) ✔ Correct; tangentiality/circumstantiality = disordered thought form. (c) ✘ Thought echo/withdrawal = passivity phenomena. (d) ✘ Nihilistic/grandiose delusions = thought content.