An element consists of two isotopes. the abundance of one isotope is 95.72% and its atomic mass is 114.9041 u. the atomic mass of the second isotope is 112.9043 u. what is the average atomic mass of the element?
a. 118.9 u
b. 113.0 u
c. 113.9 u
d. 114.8 u

d. 114.8 u

Explanation:

The formula for the calculation of the average atomic mass is:

Given that:

For first isotope:

% = 95.72 %

Mass = 114.9041 u

For second isotope:

Since the element has only 2 isotopes, so the percentage of second is 100 - first percentage.

% = 100 %  - 95.72 %  = 4.28 %

Mass = 112.9043 u

Average Mass = ?

Thus,  

Average atomic mass = 114.8 u

answer: -

reaction:

na + cl ⇌ nacl

balanced chemical equation:

na + 2cl ⇌ nacl2

sodium + clorine goes to form sodium chloride (table salt).

the product is nacl2.

and the reactants are na and cl.

(note: if you don’t know what ⇌ means, read below: -

⇌(double head arrow) means reversible reaction).