For which of the following reactions would the AHfº for the reaction be labelled AHO? (a) Al(s) + 3/2 H2(g) + 3/2 O2(g) → Al(OH)3(s)
(b) 2Al(s) + 3H2(g) + 302(g) → 2Al(OH)3(s)
(c) 1/2 N2O(g) + 1/4 O2(g) NO(g)
(d) CaO(s) + SO2(g)
CaSO3(s)

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2

answer carbon and three oxygen atoms;