Which of the following is an example of herbicide?

1. A

   Sodium chlorate

   Sodium chlorate is a non-selective herbicide and defoliant (also an oxidiser). Among the given chemicals it is the example of a herbicide, so (a) is the official key.

2. B

   Potassium permanganate

   Potassium permanganate is a strong oxidising disinfectant and titrant, not used as a field herbicide in this list.

3. C

   Bleaching powder

   Bleaching powder (CaOCl2) is a disinfectant and bleaching agent, not classified here as a herbicide.

4. D

   None of the above

   ‘None of the above’ fails because sodium chlorate is a herbicide.

Summary. Official key is (a) sodium chlorate. KMnO4 and bleaching powder are oxidisers/disinfectants, not the herbicide example on this list.