Wedges and dashes are used to indicate the shape in a drawn structure. A wedge indicates that the atom or group is of the page and a dash indicates that the atom or group is going into the page .

Wedges and dashes are used to indicate the three dimensional shape in a drawn structure.

A wedge indicates that the atom or group is GOING OUT of the page.

Explanation:

wedges and dashes are ways or drawings use to represent three dimensional shape in a structure. Lines are use to represent image in the structure. A wedge line shows that molecules or bonds are moving towards the viewer i.e out of the the page.

A dashes line shows that bonds or atom are moving away the viewer or going into the group.

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