7. Calculate the average atomic mass of bromine. One isotope of bromine has an atomic mass of 78.92amu and a relative abundance of 50.69%. The other major isotope of bromine has an atomic mass of 80.92amu and a relative abundance of 49.31%.

Average atomic mass  = 79.9 amu.

Explanation:

Given data:

Average atomic mass of Bromine = ?

Atomic mass of 1st isotope = 78.92 amu

Relative abundance of 1st isotope = 50.69%

Atomic mass of 2nd isotope = 80.92 amu

Relative abundance of 1st isotope = 49.31%

Solution:

Average atomic mass = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass  = (50.69×78.92)+(80.92×49.31) /100

Average atomic mass =  4000.45 + 3990.16 / 100

Average atomic mass  = 7990.61 / 100

Average atomic mass  = 79.9 amu.

d: the voltage of the secondary coil is less than that of the primary coil.

im not suree sorry if wrong

it is b that is the answer.