What defines one mole of a substance

Solution :

It is given that :

The formula of the compound =

And that 4.70 g of the sample contains mol of Br.

It means that :

1 mol of contains = 3 mol of Br

∴ 3 mol of contain in 1 mol of

mol of  contains mol of

Thus the mol of = mol

The given mass is = 4.700 g

Therefore, the of  

                                                          = 298.4 g/mol

So of = of X + 3 x of Br

      298.4 g/mol = of X + 3 x 79.90 g/mol

      298.4 g/mol = of X + 239.7 g/mol

        of X = 58.71 g/mol    (since 1 amu = 1 g/mol)      

Therefore the atomic mass of the unknown metal = 58.71 g/mol

So the unknown meta is Nickel.