To draw lewis structure of each of the compound, determine the number of electrons of valence of each element. To do it we can take a look to the electron configuration of each element.
a)NF3. According to nitrogen electron configuration, it has 5 electrons of valence and according to fluorine configuration, it has 7.
Lewis structure for this compound is:
b)ClO3. Chlorine has 7 electrons of valence and oxygen has 6. This is an ion, so it has a charge, that has to be expressed as follows:
c)HOBr. Bromine has 7 electrons of valence, oxygen has 6 and hydrogen 1:
d)SO3. Sulfur has 6 electrons of valence and oxygen has 6 too:
