Who among the following may not testify?

Option (1) is incorrect: Accomplice is competent to testify. As Section 118 says that all persons shall be competent to testify unless the court considers that they are prevented from understanding the question put to them, or from giving rational answers to those questions, by tender years, extreme old age, disease, whether of body or mind, or any other cause of the same kind. Option (2) is incorrect: Under the Indian Evidence Act, a child is competent to testify if he can understand the questions put to him or give rational answers. Option (3) is incorrect: Under the Indian Evidence Act, a dumb person is competent to testify if he can understand the questions put to him or give rational answers whether orally or in writing.  Option (4) is correct. Under the Indian Evidence Act, a lunatic who is not able to understand the question and to give a rational answer is not competent to testify.