1. The problem statement, all variables and given/known data (i) An element that has a molecule which contains exactly four atoms. (ii) An element that reacts with water to give a solution that can behave as an oxidising agent. 2. Relevant equations 3. The attempt at a solution (i) Shouldn't it be boron? Boron forms BF3 which has four atoms. (ii) Mg? Because Mg forms Mg+2 ions when it forms an oxide/hydroxide with water. This will cause it to reduce itself, oxidising other compounds, making it an oxidising reagent.