Question

which of the following elements would you expect to be stable and why?
2A⁴, 11B²³, 13C²⁷, 20D⁴⁰​

Answer 1

Answer:

2A'4 = He

11B'23 = Na

13C'27 = Al

20D'40 = Ca

all below He are reactive metal due to incomplete outershell

but,

'He(helium) ' have complete shell with 2 electrons and it is Nobel gas. so it is less reactive

reactivity inversely proportional to stability.

so, He more stable.