next question number 4 to 9..

4.Write the isotopes notation for krypton-78. Given that the proton number of Kr is 36.

= Kr

5.What is the average atomic mass of element X if X consists of 78.7% of atom with a mass of 24.0 amu, 10.1% of atoms with a mass of 25.0 amu and 11.2% of atoms with a mass of 26.0 amu?

Average atomic mass =

=

=

=25.17 amu

6.Calculate average atomic mass of Neon.

Average atomic mass =

=
=20.19 amu

7. a)percentage =

b) Ar =

=

= 35.5

8. Ar =

x=60.112amu

Ga-69=60.112 Ga-71= 100-60.112 =39.888

9. percentage of B-10 = 19.9%

B-11 = 100- 19.9

= 80.1%

Ar =

10.811=(19.9 x 10.0219) + (801 x X)

19.9 + 80.1

x=11.087 amu