The volume occupied by an atom is greater than the volume of the nucleus by a factor of about
$10^1$
$10^5$
$10^{10}$
$10^{15}$
A nucleus represented by the symbol ${ }_{Z}^{ A } X$ has
The mass of an $\alpha$-particle is
Which of the following pairs is an isobar
$(a)$ Two stable isotopes of lithium $_{3}^{6} L$ and $_{3}^{7} L$ have respective abundances of $7.5 \%$ and $92.5 \% .$ These isotopes have masses $6.01512\; u$ and $7.01600\; u ,$ respectively. Find the atomic mass of lithium.
$(b)$ Boron has two stable isotopes, $_{5}^{10} B$ and $^{11}_{5} B$. Their respective masses are $10.01294 \;u$ and $11.00931\; u$, and the atomic mass of boron is $10.811\; u$. Find the abundances of $_{5}^{10} B$ and $_{5}^{11} B$
Write the definition of $Z, A$ and $N$ by stating the structure of a atom.