Please help with chemistry... exo and endothermic?!?

CuHAsO4 would be expected to be an ionic compound consisting of Cu+ cations and HAsO4- anions. This is because metals often form ionic compounds with anions formed by deprotonation of an oxoacid (in this case H2AsO4). Lead hydrogen arsenate is a known, ogous compound. In the case of (CH3)3As, one might guess a molecular compound because CH3 does not form a stable ion. You can draw a Lewis dot structure for (CH3)3As to try to justify it further.