3.A sample of chlorine contains 75% of 35 17Cl and 25% of 37
17Cl.
Calculate the relative molecular mass of chlorine.

35.5

Explanation:

Given parameters:

Abundance of chlorine Cl  - 35 = 75%

Mass of Cl - 35 = 35

Abundance of Cl - 37  = 25%

Mass of Cl - 37 = 37

Unknown:

Relative molecular mass  = ?

Solution:

The relative molecular mass of the chlorine can be deduced using the expression below:

   Relative molecular mass  = (abundance x mass of Cl - 35) + ( abundance x mass of Cl - 37)

 Relative molecular mass  = (75% x 35) + (25% x 37)  = 35.5

the answer is definitely c.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.