How are these chemistry equations incorrect and how can they be fixed

1. Mg+2F --> MgF2
2. NaI+Cl2 --> NaCl+I
3. Mg+HCl -->H2+MgCl
4. H2+Cl2 --> H2Cl2
Also, what are the coefficients of each equation, as I am not sure what the word coefficient is referring to..

1. correct

2. Cl2 + 2NaI ---> 2NaCl + I2

3. Mg + 2HCl ----> H2 + MgCl2

4. H2 + Cl2 -----> 2HCl

The coefficient (the number before a molecule) of each equation is 2.