Calculate average atomic mass: 25% c-11, 25% c-14

6.25 amu

Explanation:

Data Given:

Abundance of C-11 = 25 % = 0.25

mass of carbon-11 = 11 amu

Abundance of C-14 = 25 % = 0.25

mass of carbon-14 = 14 amu

Average atomic mass = ?

Solution:

formula used to check average atomic mass is as under

                          Average atomic mass = m₁A₁ + m₂A₂

Where

m₁ and m₂ = mass of isotope 1 and 2 respectively

A₁ and A₂ = abundance or fraction of isotope 1 and 2 respectively

Put values in above formula

                   Average atomic mass = (11 amu)(0.25) + (14 amu)(0.25)    

                   Average atomic mass = 2.75 + 3.5

                   Average atomic mass = 6.25 amu

So

Average atomic mass of 25% C-11, 25% C-14 = 6.25 amu

it's all four options.