State that ammonium salts and nitrates are used as fertilisers

Describe tests using aqueous sodium hydroxide and aqueous ammonia to identify the aqueous cations: (a) aluminium, ( Al^{3+} ) (b) ammonium, ( NH_4^+ ) (c) calcium, ( Ca^{2+} ) (d) chromium(III), ( Cr^{3+} ) (e) copper(II), ( Cu^{2+} ) (f) iron(II), ( Fe^{2+} ) (g) iron(III), ( Fe^{3+} ) (h) zinc, ( Zn^{2+} )