Question
Elements $$X, Y$$ and $$Z$$ have atomic numbers $$19, 37$$ and $$55$$ respectively. Which of the following statements is true about them ?
A.
Their ionization potential would increase with increasing atomic number
B.
$$'Y'$$ would have an ionisation potential between those of $$'X'$$ and $$'Z'$$
C.
$$'Z'$$ would have the highest ionization potential
D.
$$'Y'$$ would have the highest ionization potential.
Answer :
$$'Y'$$ would have an ionisation potential between those of $$'X'$$ and $$'Z'$$
Solution :
Elements $$X, Y, Z$$ with atomic numbers $$19, 37, 55$$ lie in group 1 (alkali metals). On moving down a group from the size of atoms increases, the outermost electrons become less strongly held. So the ionization energy decreases. Therefore, $$IE$$ of $$Y$$ could be between those of $$X$$ and $$Z.$$
\[\begin{matrix}
{} \\
{} \\
I.E. \\
\end{matrix}\,\,\,\begin{matrix}
X \\
K\left( 19 \right) \\
4.3 \\
\end{matrix}\,\,\,\begin{matrix}
Y \\
Rb\left( 37 \right) \\
4.2 \\
\end{matrix}\,\,\,\begin{matrix}
Z \\
Cs\left( 55 \right) \\
3.9 \\
\end{matrix}\]