3. in which of the following are the symbol and name of the ion given correctly? *
a. nh4^+: ammonia; h^+: hydride
b. oh^-: hydroxide; o^-2: oxide
c. po3^-3: phosphide; po4^-3: phosphate
d. no3^-: nitrite; n^-3: nitride
4. why are systematic names use more than common names? *
a. common names were assigned by the scientist who discovered the compound
b. common names are not very descriptive
c. common names are derived from the method used to manufacture the compound
d. common names do not provide information about the chemical make-up of the compound

the answer to this question is 3.

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