Isotopes are the atoms of same element: they have same atomic number but different mass numbers. Isoto have different number of neutrons in their nucleus. If an element exists in two isotopes having atomic mas 'a' and 'b' in the ratio m:n, then average atomic mass will be `( m xx a + n xx b)/( m + n)`
Different isotopes of same element have same position in the periodic table. The elements which have sin isotope are called monoisotropic elements. Greater is the percentage composition of an isotope, more wiki be its abundance in nature.
An element, X has the following isotopic.composition. `""^(2)X:90%,""^(109)X,8% ""(202)X,2%.` The weight average atomic mass of the naturally occurring element 'X' is closest to:

Options

A. 20.1 amu
B. 20.2 amu
C. 14.6 amu
D. 20 amu

Answer

D

Explanation

Average atomic mass of `X = [(90)/( 100) xx 200 ]+ [ (8)/(100 ) xx 199] + [ (2)/(100 ) xx 202] = 199.96 = 200 ` amu