Which of the two metal ions mg2+ and zn2+ is the most reactive why?

Mg2+

Explanation:

The most reactive ions from the given choices is the magnesium ion. This is because it is higher in the activity series of metals.

Zinc ion is below this specie in the activity series.

As a rule, ions above another on the activity series are generally more reactive than those below.

From any solution, magnesium ion will displace the zinc ion in such process.

The position of metallic ions determines their reactivity.

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