atomic mass of magnesium = 24.305
atomic mass of chlorine = 35.453
molecular mass of MgCl2 = 24.305+2*35.453 = 95.211
Number of moles in 338 g of pure MgCl2
= 338/95.211 = 3.55001 moles
Ans. there are 3.55 moles of MgCl2 in 338 g of the substance.
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