The true answer is: It's conserved because the total number of H atoms on each side is 12.
the first two answer is wrong because it's conserved not as mentioned, It's not conserved.
and the last one also wrong because the total number of O atoms are equal at the two sides but not equal 2.
Cr2(CO3)3 is Chromium (III) Carbonate or Chromic Carbonate.
It is composed of Chromium, Carbon, and Oxygen. Chromium has 2 atoms, Carbon has 3 atoms, and Oxygen has 9 atoms.
This compound is composed of 36.6% Chromium, 12.7% Carbon, and 50.7% Oxygen.
A variable is not consistent or having a fixed pattern; liable to change.
TBH i dont know but can you give advice to get more points on this site