Which is true about each element in a period or horizontal row of the periodic table? a. each element has one more outer shell than the element before it. b. each element has one more outer electron than the element before it. c. each element has one more isotope than the element before it. d. each element bonds with the element before it.

The answer is B as going from left to right on the periodic table elements increase by 1 in valence electrons

Valence electrons : The electrons on the outermost shell

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