Answer:
NiCl₂·4H₂O, its name being nickel (II) chloride tetrahydrate.
Explanation:
The constant mass achieved after heating is the mass of anhydrous nickel (II) chloride, NiCl₂. While the mass lost was water.
Now we convert 0.750 g of NiCl₂ into moles, using its molar mass:
Then we convert 0.417 g of H₂O into moles:
With the above information we can calculate that the number of H₂O moles is 4 times higher than the number of NiCl₂ moles.
Meaning that the formula of the hydrate is NiCl₂·4H₂O, its name being nickel (II) chloride tetrahydrate.