A change in pH of 1.0 unit indicates that: a. the molarity of H changes by one order of magnitude.
b. the acid or base content decreases or in- creases by 0.1 M.
c. the acid or base content decreases or in- creases by 1.0 M.
d. the salt content decreases or increases by 1.0 M.
e. the volume of H in a solution changes by an order of magnitude.

e is the answer

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

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