How would your calculated value for the % NaHCO3, have been affected if you didn't add enough acid to the solution?
NaHCO3 + HCl → NaCl + H2O(l) + CO2(g)
a) The percentage of sodium hydrogen carbonate would be too low.
b) The percentage of sodium hydrogen carbonate would be too high.
c) The percentage of sodium hydrogen carbonate would be unchanged.
d) It could be either too high or too low.

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).

the answer to your question is c

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