Elements X, Y and Z have atomic numbers 19,37 and 55 respectively. Which of the following statements is true…

Elements X, Y and Z have atomic numbers 19,37 and 55 respectively. Which of the following statements is true about them ?
  1. Their ionization potential would increase with increasing atomic number
  2. 'Y' would have an ionisation potential between those of ' $X$ ' and ' $Z$ '
  3. 'Z' would have the highest ionization potential
  4. 'Y' would have the highest ionization potential.

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 $Z$.
$$
\begin{array}{lll}
\mathrm{X} & \mathrm{Y} & \mathrm{Z} \\
\mathrm{K}(19) & \mathrm{Rb}(37) & \mathrm{Cs}(55) \\
4.3 & 4.2 & 3.9
\end{array}
$$
I.E 43

Asked in: JEE-TOPICTESTS-CHEMISTRY

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