Look at the periodic table to find the charge on atoms.
Magnesium is +2 and Nitrogen is -3. Since there are two nitrogen charge 2*-3 = -6 there needs to be 3 Mg then (3*2+ = 6+) to pair with the two nitrogen.
3 Mg(+2) + 2 N(-3) = Mg3N2
The most appropriate answer is C !!
The molar mass is usually referred to with
M
, while the mass is referred to as
m
. The amount of substance is
n
. This gives you the following relationship:
=
M
=
m
n
Since you have given (C3H8)=11 g
m
(
C
3
H
8
)
=
11
g
and you already looked up (C3H8)=44.1 gmol−1
M
(
C
3
H
8
)
=
44.1
g
m
o
l
−
1
, you can use this formula to determine (C3H8)
n
(
C
3
H
8
)
.
In this question it is quite hard to explain the use of significant figures. Those are used to imply a certain inaccuracy. Not enough information is given by the question, as of how accurate the measurement is. It is a mere exercise of converting one property into another. Here you should not worry about it.
