Which one of the following elements has the least ionisation energy?

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Solution

The correct option is A
Cs

Ionisation energy is the minimum amount of energy required to remove the most loosely bound electron i.e the valence electron, of an isolated neutral, gaseous, atom.

Among the given choices, caesium has the largest atomic radius and maximum metallic character. Hence, it is easiest to extract an electron from it, i.e., it has the least ionisation energy.

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Similar questions

Which element from the following has the highest ionisation energy ?

(a) P, Na, Cl (b) F, O, Ne (c) Ne, He, Ar

Explain your choice.

Arrange the following as per instructions given in the brackets.

(a) Mg. Cl, Na, S, Si (decreasing order of atomic size)

(b) Cs, Na, Li, K, Rb (increasing metallic character)

(d) Cl, F, Br, I (increasing electron affinity)

(e) Cs, Na, Li, K, Rb (decreasing electronegativity)

L i^{+}

N a^{+}

C s^{+}

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