Question

please answer this question!!

thanks :)

Answer 1

Heya 

:) Honored to answer a BS √√

--> The Alphabetical representation hides the identity of the element in the qn.. sooo, it'll be better to avoid identifying them ( just for impression .. or showing that uh have a good concept of that Chapter +_+ )

( i ) very stable :->


--> For the stability, valency = 0.. , i.e., the outermost shell electrons completely fill it..
 
--> So far, the electronic config. goes --> 2 , 8 , 8 , 2 ( Highest of A )

Now, 1st shell ( max ) = 2
----> 2nd shell ( max ) = 8
----> 3rd shell ( max ) = 8 ...

And so we see.. 
$_{2}F .. \ which \ is \ actually \ Helium \ is \ the \ most \ stable \ one ...$

Again, for --> 2, 8, 8 ( total 18 electrons.. )
$_{18}C .. \ which \ is \ actually \ Argon \ is \ the \ most \ stable \ one ...$

Note :-> These are Noble Gases... Helps to identify easily.. :)

( ii ) group 2 element :->

--> Group 2 elements are alkaline earth metals and a sound knowledge of Chemistry can easily help uh determine that it is ... $_4E \ which \ is \ Berrylium \ and \ _20A \ which \ is \ Calcium$

--> However, if u're not that interested... Just know the valency Be(2+) and Ca(2+) ... and so, you get ur ans

( iii ) in group 16
---> Group 16 is oxygen family.. chalcogens..
---> Simple counting can get uh that Atomic no. '8' belongs to it..
And so, 
$_8B \ which \ is \ Oxygen \ is \ the \ answer$

( iv ) What kind of bond ....
--> A has atomic no. '20' and so, it's Calcium while 'B' is Oxygen..

Clearly, Calcium Oxide is an Ionic Compound and therefore Ionic Bond... But you can use the Atomic no. or the '2nd' and '2nd last' Group no. that defines their Bond type !!

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Hope this helped ^_^ 

( Ugh.. I wonder if uh also need the answer to 20. (a) ..
In case uh do.. -->
---> Seperation of Oxygenated and Deoxygenated blood .. which defines the double circulation system .. is  :->
( i ) more likely essential for the efficiency of the Circulatory system and
( ii ) maintaining the Body Temperature ( observing the hot... and cold... bloodedness of different species.. )

^_^