The number of hydrogen atoms in an alkane molecule with a relative molecular weight of 100 is …

Alkanes are called saturated hydrocarbons with the general formula CnH2n + 2.

Relative atomic mass of carbon = 12, relative atomic mass of hydrogen = 1

The molecular weight of a substance for the general formula will be calculated as follows: 12 * n + 1 * (2n + 2)

In our case, the molecular weight is known, which means you can write an equation with one unknown and solve it:

12 * n + 1 * (2n + 2) = 100

12n + 2n +2 = 100

14n + 2 = 100

14n = 100 – 2

14n = 98

n = 98/14

n = 7

So our substance has the formula C7H16 (heptane). Let’s check: 12 * 7 + 1 * 16 = 100

The number of hydrogen atoms in a heptane molecule is 16