NaCl: natriumchloride. 1 atom of each, so the 2 is too much and I (capital i here) is another element
So for the second excercise the number behind the symbol is the amount of atoms in the compound. So easily 2 atoms of Li, 1 atom of S and 4 of O
The importance of the International System of Measurement is important because it provides the same values for measurements such as length, weight, and time no matter where in the world the measurement is performed.
If the disease was cause by the dominant allele, every person with said gene would be affected with the disease. if the genetic allele is recessive, both parents can be carriers (hetero) without being affected. that makes it easier for the genes to keep being passed on.
hope this helps!