The table below gives the atomic mass and relative abundance values for the three isotopes of element [tex]\( M \)[/tex].

[tex]\[
\begin{array}{|c|c|}
\hline
\text{Relative abundance (\%)} & \text{Atomic mass (amu)} \\
\hline
78.99 & 23.9850 \\
\hline
10.00 & 24.9858 \\
\hline
11.01 & 25.9826 \\
\hline
\end{array}
\][/tex]

What is the average atomic mass (in amu) of element [tex]\( M \)[/tex]?

A. 2.86

B. 5.36

C. 24.30

D. 24.98



Answer :

To calculate the average atomic mass of element [tex]\(M\)[/tex], we can use the weighted average formula based on the given relative abundances and atomic masses of the isotopes.

Here are the values from the table:

1. Relative abundance = 78.99%, Atomic mass = 23.9850 amu
2. Relative abundance = 10.00%, Atomic mass = 24.9858 amu
3. Relative abundance = 11.01%, Atomic mass = 25.9826 amu

Let's convert these percentages to fractional abundances by dividing by 100:

1. [tex]\( \text{Abundance}_1 = \frac{78.99}{100} = 0.7899 \)[/tex]
2. [tex]\( \text{Abundance}_2 = \frac{10.00}{100} = 0.1000 \)[/tex]
3. [tex]\( \text{Abundance}_3 = \frac{11.01}{100} = 0.1101 \)[/tex]

Next, we apply the formula for the weighted average:

[tex]\[ \text{Average atomic mass} = (\text{Abundance}_1 \times \text{Mass}_1) + (\text{Abundance}_2 \times \text{Mass}_2) + (\text{Abundance}_3 \times \text{Mass}_3) \][/tex]

Plugging in the values:

[tex]\[ \text{Average atomic mass} = (0.7899 \times 23.9850) + (0.1000 \times 24.9858) + (0.1101 \times 25.9826) \][/tex]

Performing the multiplications:

1. [tex]\( 0.7899 \times 23.9850 = 18.9584115 \)[/tex]
2. [tex]\( 0.1000 \times 24.9858 = 2.49858 \)[/tex]
3. [tex]\( 0.1101 \times 25.9826 = 2.84802426 \)[/tex]

Adding these results together:

[tex]\[ 18.9584115 + 2.49858 + 2.84802426 = 24.30501576 \][/tex]

Therefore, the average atomic mass of element [tex]\(M\)[/tex] is [tex]\( \boxed{24.30} \)[/tex] amu.