boron has an average atomic mass of 10.81. one isotope of boron has a mass of 10.012938 and a relative…

Explanation:

Step1: Set up the formula for average atomic mass

The formula for average atomic mass $A$ is $A = m_1\times p_1 + m_2\times p_2$, where $m_1$ and $m_2$ are the masses of the isotopes and $p_1$ and $p_2$ are their relative - abundances (in decimal form). Let $m_1 = 10.012938$, $p_1=0.1980$, $p_2 = 0.8020$, and $A = 10.81$. We need to find $m_2$.

Step2: Rearrange the formula to solve for $m_2$

Starting from $A = m_1\times p_1 + m_2\times p_2$, we can rewrite it as $m_2=\frac{A - m_1\times p_1}{p_2}$. Substitute the given values: [ \begin{align*} m_2&=\frac{10.81-(10.012938\times0.1980)}{0.8020}\ &=\frac{10.81 - 1.982561724}{0.8020}\ &=\frac{8.827438276}{0.8020}\ &\approx11.01 \end{align*} ]

Answer:

$11.01$