The unknown element (Johnsonium, Jo) contains three naturally occurring isotopes. The relative abundances and atomic mass are: Moorium-36: abundance = 1.32%, mass = 35.978amu
Moorium-38: abundance = 3.25%, mass = 37.963amu
Moorium-40: abundance = 95.43%, mass = 39.962amu
What is the average atomic mass of "Moorium?"

Average atomic mass of moorium is 39.844 amu.

Explanation:

Given data:

Atomic mass of moorium-36 = 35.978 amu

Relative abundance of  moorium-36 = 1.32%

Atomic mass of moorium-38 = 37.963 amu

Relative abundance of  moorium-38 = 3.25%

Atomic mass of moorium-40 = 39.962 amu

Relative abundance of  moorium-38 = 95.43%

Solution:

Average atomic mass moorium = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)+ (abundance of 3rd isotope × its atomic mass)  / 100

Average atomic mass of moorium = (1.32×35.978)+(3.25×37.963)+(95.43×39.962) /100

Average atomic mass of moorium =  47.491 + 123.380 +3813.574  / 100

Average atomic mass of moorium = 3984.445 / 100

Average atomic mass of moorium = 39.844 amu

a electronegativity decreases beacuse the size of nucleus is bigger.