Electronicconfiguationof four elements B, C and Dare givenbelow : A. 1s^(2)2s^(2)2p^(6)B. 1s^(2)2s^(2) 2p^(4) C. 1s^(2)2s^(2)2p^(6)3s^(1)D.1 s^(2)2s^(2)2p^(5) whichof the followingis thecorrectorderincreasingtendencyto gainelectron :

Electronicconfiguationof four elements B, C and Dare givenbelow : A. 1

1.	Electronicconfiguationof four elements B, C and Dare givenbelow : A. 1s^(2)2s^(2)2p^(6)B. 1s^(2)2s^(2) 2p^(4) C. 1s^(2)2s^(2)2p^(6)3s^(1)D.1 s^(2)2s^(2)2p^(5) whichof the followingis thecorrectorderincreasingtendencyto gainelectron :
Answer» `A lt C lt B lt D` `A lt B lt C lt D` `D lt B lt C lt A` `D lt A lt B lt C` Solution :Electronicconfigurationsof elementssuggestthat A is a noblegas (i.e., Ne) B is oxygen(Group 16), Cis an ALKALI metal( group1) andDis a halogen( group 17) . (i) Noblegases have no tendencyto gain electronssince alltheirorbitalsare completely FILLED. Thuselement A hashte leastelectron gainenthalpy. Nowsinceelement D hasone electron lessand elementBhastwoelectrons LESSTHAN thecorrespondingnoblegasconfigurationthereforeelementD hasthe highestelectrongainenthalpyfollowedby ELEMENT B. (iii) SinceelementC hasoneelectron in thes-orbitaland henceneedsone moreelectron to complete it thereforeelectrongainenthalpy of C islessthan that of elementB. Combing all the factsgivenabovetheelectron gain enthalpy of thefour elementsincreasesin theorder `: A lt C lt b lt D,` i.e.,option (a) is correct .