Choose from the following elements to answer the questions. aluminium carbon hydrogen iron magnesium nitrogen oxygen sodium vanadium Each element may be used once, more than once or not at all. Which element:

1. (a)(i)is a catalyst in the Haber process,[1]
2. (a)(ii)makes up 21% of dry air,[1]
3. (a)(iii)can be formed when hydrocarbons are cracked,[1]
4. (a)(iv)forms aqueous ions with a 3+ charge which give a white precipitate when added to aqueous ammonia,[1]
5. (a)(v)has an atom with only three electrons in its outer shell?[1]
6. (b)Complete the table to show the number of electrons and neutrons in the potassium atom and in the oxide ion. number of electrons number of neutrons 41 19K 17O2- 8O2-[4]