What new characteristic did john dalton add to the model of the atom? (a) an atom is a round, solid mass.(b) an atom has a massive, positive center. (c)an atom is made up of smaller particles.(d) an atom can join with other kinds of atoms.

The right answer is D.

John Dalton is a British chemist and physicist who developed the atomic theory on which modern physical science was based.

The atom is, for chemists, the fundamental constituent of matter. The term comes from elsewhere a Greek word that means "indivisible", although it is known for a long time that this element is not.

The atom may be associated with other atoms, similar or different, to form a molecule (two oxygen atoms to form O2, or two hydrogen atoms with an oxygen atom to form H2O)

Basically he explained the principle of what is a molecule. He was wrong thinking that atoms are indivisible particles.

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