Question

Indium (atomic weight = 114.8) has two naturally occurring isotopes, the predominant one form has
isotopic weight 115 and abundance of 95.00%. Which of the following isotopic weights is the most likely
for the other isotope ?
(A) 111
(B) 112
(C) 113
(D) 114

ans is option a explain it plz​

Answer 1

Answer: A) 111

Explanation:

Given average mass of Indium = 114.8

Mass of isotope 1 = 115

% abundance of isotope 1 = 95% = $\frac{95}{100}=0.95$

Mass of isotope 2 = ?

% abundance of isotope 2 = (100-x)% = $\frac{100-95}{100}=0.05$

Formula used for average atomic mass of an element :

$\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})$

$114.8=[115\times 0.95+M\times 0.05]$

$M=111$

Therefore, the isotopic weights for the other isotope is 111.

Answer 2

Answer:

1) 111

Explanation:

Abundance of first element =95%

= 95/100 = 0.95

Abundance of second element = 100-95

= 5%

= 5/100 = 0.05

Let X be the mass of second isotope

= 115×0.95+X×0.05 = 114.8

= 114.8-109.25/0.05

= 111

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Hope it helps !!!