Dana wants to determine the molar mass of magnesium hydroxide, mg(oh)2. which calculation should she use?

a) (atomic number of mg) + (2 x atomic number of o) + (2 x atomic number of h)
b) 2 x (atomic number of mg + atomic number of o + atomic number of h)
c) (molar mass of mg) + (2 x molar mass of o) + (2 x molar mass of h)
d) 2 x (molar mass of mg + molar mass of o + molar mass of h)

C is correct

Explanation:

The molar mass is the total mass of a compound, that means, you need to add the mass of every single atom in the formula. In this case, you have one atom of Magnesium, two atoms of Oxygen and two atoms of Hydrogen, that is the reason why you need to multiply molar mass x 2 in the case of Oxygen and Hydrogen

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer