Ionisation energy in group $1 A$ varies in the decreasing order as:

L i > N a > K > C s

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N a > L i > K > C s

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L i > C s > K > N a

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K > C s > N a > L i

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Solution

The correct option is D $L i > N a > K > C s$
Atomic size increases as we move from top to down in a group, therefore, the amount of energy required for ejection of an electron from atom decreases, i.e. ionisation energy decreases. Hence, the correct order of $I E_{1}$ is
$L i > N a > K > C s$ .

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Similar questions

The correct order of reactivity of alkalimetals towards $H_{2}$ is

L i^{+}

N a^{+}

C s^{+}

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^{+} < K^{+} < C s^{+}

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