You are given the solution of lead nitrate. In order to obtain a yellow precipitate you should mix with it a solution of:

36 One of the following does not happen during a chemical reaction. This is: 37 Which of the following does not involve a chemical reaction? 39 An acid which can decolourise purple coloured potassium permanganate solution is: 40 The chemical reaction between two substances is characterised by a change in colour from orange to green.

These two substances are most likely to be: