Which one of the following is not an explosive matter ?

Go with D. Nitrochloroform, also called chloropicrin (CCl3NO2), is a toxic liquid used as a soil fumigant and pesticide. It was also a chemical warfare agent in World War I. It is dangerous, but it is not a detonating explosive, so it does not belong with the others.

The other three are explosives:

• Trinitrotoluene (TNT): a nitroaromatic high explosive and the standard benchmark for explosive power.
• Nitroglycerine: the intended compound in option B, a nitrate ester used in dynamite. The name 'dinitro glycerine' is a slip in the option; the trinitrate is the explosive.
• Cyclotrimethylenetrinitramine (RDX): a cyclic nitramine and a major military high explosive.

Core concept: explosives are compounds carrying nitro or nitrate groups in a structure that decomposes rapidly and releases large energy in a detonation. Nitrochloroform has a nitro group, but its use and behaviour are those of a toxic agent, not a high explosive. This links to the Mains theme of dual-use chemicals and internal security regulation.

Trap: candidates see 'nitro' in the name and mark it explosive. A nitro group alone does not make a compound explosive; the molecular structure and energy release decide it.