Import Question JSON

$\text{HINT: Reactivity of metal } \propto \frac{1}{\text{Ionisation energy}} \propto \text{ Electron affinity}$ $\text{Explanation:}$ $\text{The elements present in group 1 have only 1 valence electron, which they tend to lose. Group 17 elements, on the other hand, need only one electron to attain the noble gas configuration. On moving down group 1, the ionization enthalpies decrease. This means that the energy required to lose the valence electron decreases. Thus, reactivity increases on moving down a group.}$ $\text{Thus, the increasing order of reactivity among group 1 elements is as follows: Li < Na < K < Rb < Cs}$ $\text{In group 17, as we move down the group from Cl to I, the electron gain enthalpy becomes less negative i.e., it's tendency to gain electrons decreases down group 17. Thus, reactivity decreases down a group. The electron gain enthalpy of F is less negative than Cl. Still, it is the most reactive halogen. This is because of its low bond dissociation energy.}$ $\text{Thus, the decreasing order of reactivity among group 17 elements is as follows: F > Cl > Br > I}$ $\text{Detailed analysis:}$ $\text{For alkali metals (Group 1):}$ $\text{• Reactivity depends on ease of losing the single valence electron}$ $\text{• As atomic size increases down the group, ionization energy decreases}$ $\text{• Lower ionization energy = easier to lose electron = higher reactivity}$ $\text{• Therefore: Li < Na < K < Rb < Cs (increasing reactivity)}$ $\text{For halogens (Group 17):}$ $\text{• Reactivity depends on tendency to gain one electron}$ $\text{• As atomic size increases down the group, electron gain enthalpy becomes less negative}$ $\text{• Less negative electron gain enthalpy = lower tendency to gain electron = lower reactivity}$ $\text{• Therefore: F > Cl > Br > I (decreasing reactivity)}$ $\text{The correct option is 1: ionization enthalpy decreases in group 1 while electron gain enthalpy becomes less negative in group 17.}$