Pretty sure the answer is c but not completely positive !
Number of moles of Hydrogen gas produced = 2.5 moles
Given the balanced chemical equation,

This means, 1 mole of Mg and 2 moles of HCl gives 1 mole of Hydrogen gas.
Given that 2.5 moles of Magnesium is taken and an excess of Hydrochloric acid.
The mole ratio of Magnesium and Hydrogen = 1:1
Thus 2.5 moles of Magnesium with an excess of Hydrochloric acid will yield 2.5 moles of Hydrogen gas.
[By referring excess of HCl, we may assume that it contains at least 5 moles of HCl. Then only 2.5 moles of Mg will produce 2.5 moles of Hydrogen gas].
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Answer:
c
Explanation:
because it decrese the activation energy
Answer
Part A:
Given equation:

The above equation is an example of a double replacement reaction. A double replacement (or double displacement) reaction is a reaction in which the positive and negative ions of two ionic compounds exchange.
Note: The oxidation number of:
K = +1
I = -1
Ba = +2
S = -2
So, the complete chemical equation including phases of the given reaction is:

Part B:
Given equation:

Also, the equation is an example of a double replacement reaction.
Note: The oxidation number of:
K = +1
Cl = -1
Ca = +2
S = -2
The complete chemical equation including phases of the given reaction is: