ii)State whether you would expect the following Group 13 metal cations to act as Lewis acids or bases. Order the cations in terms of softest to hardest. Explain your answer. Al3+, Tl3+, Ga3+, Tl+ (iii) State whether you would expect the following Group 15 hydrides to act as Lewis acids or bases. Order the hydrides in terms of softest to hardest. Explain your answer. PH3, NH3, AsH3 Solution ii) The given group 13 metal cations will act as a Lewis acids , because cations are are electron deficient and act as a electron acceptor. Hard Acids are Lewis acid which are small in size and most likely are the light metal cation with high positive oxidation state like Al 3+ Soft Acids are Lewis acid which are larger in size and most likely are the heavy metal cation associated with low oxidation state like Tl 3+ Tl + Oder of cation from softest to hardest   Tl + < Tl 3+ < Al 3+ (iii) The given Group 15 hydrides will acts as Lewis Base, because Nitrogen, Phosphorus and Arsenic has a lone pair of electron that it can donate. Hard Base are Lewis base anions or neutral molecules which are not easily polarizable like NH 3 Soft Base are Lewis base anions or neutral molecules which are easily polarizable like PH 3 and AsH 3 Order the hydrides in terms of softest to hardest AsH 3 < PH 3 <NH 3 .