In plants, algae, and some bacteria, energy is produced by the: A. nucleus
B. chloroplast
C. vacuole
D. mitochondria

D?  

Explanation: The mitochondrion (plural mitochondria) is a membrane-bound organelle found in the cytoplasm of eukaryotic cells. It is the power house of the cell; it is responsible for cellular respiration and production of (most) ATP in the cell.

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