What is the chemical name of saltpetre?

Potassium nitrate

The correct answer is option 1. Potassium nitrate.

The chemical name of saltpetre is Potassium nitrate

Here's why:

Saltpetre is a common name for a naturally occurring mineral composed of potassium nitrate (KNO₃).

Potassium manganite (KMnO₄) is a different compound known as potassium permanganate, which has a distinct purple color and various uses, but is not commonly referred to as saltpetre.

Lead nitrate (Pb(NO₃)₂) and lead sulfate (PbSO₄) are compounds containing lead and are not related to saltpetre.

Therefore, potassium nitrate is the accurate name for the chemical compound commonly known as saltpetre.