(image attached) what mistake did carl make?

A) He did not multiply with calcium atoms by the subscript 2.
B) He did not add the coefficient 4 to the chlorine and oxygen atoms.
C) He did not add the subscript 2 to the calcium atoms.
D) He did not multiply the chlorine and oxygen atoms by the coefficient 4.

(pls answer question with letter choice as well as explaination)

D) He did not multiply the chlorine and oxygen atoms by the coefficient 4.

Explanation:

The coefficient 4 at the beginning of the chemical formula indicates that there are four Ca(ClO3)2 molecules. Think of this as Ca(ClO3)2 × 4. This means that he had to multiply the number of atoms for each element by 4 as well, so he should've ended up with 4 total calcium atoms (which is correct), 8 total chlorine atoms, and and 24 total oxygen atoms. He did not get all these answers because he didn't multiply the chlorine and oxygen atoms by the coefficient 4.

the reaction mixture contains some ammonia, plus a lot of unreacted nitrogen and hydrogen. the mixture is cooled and compressed, causing the ammonia gas to condense into a liquid. the liquefied ammonia is separated and removed. the unreacted nitrogen and hydrogen are then recycled back into the reactor .

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.