Need calculating the molecular weight and finding the correct formula for

1.) barium sulfide
sodium acetate
potassium phosphate

2.)which of the following contains both ionic and covalent bonds? which are purely ionic? which have only covalent bonds?

h3po4
kno3
nh3
kcl
co2

3.) rank the following compounds from smallest to largest lattice energy. (lowest to highest melting point.)

cao, csi, bas, naf, nacl

4.) can you show me the calculation part when determining how any valence electrons for these
sih4
brf3
h2co

i can draw the lewis structure for each one after that from here also do you know how many lone and bond pairs does formaldehyde have