Error Analysis — NEET Traps & Common Mistakes — Notes

#	Trap / Error	Wrong Thinking	Correct Reasoning
1	"F has most negative EGE among halogens"	F is most electronegative → best $e^{-}$ acceptor	EGE(Cl) = −349 > EGE(F) = −328. F's small 2p causes $e^{-}$ – $e^{-}$ repulsion
2	"IE increases uniformly across Period 2"	Zeff always rises L→R	Exceptions: IE(Be) > IE(B) and IE(N) > IE(O)
3	"Cation is larger than its neutral atom"	Adding charge doesn't matter	Cation loses electrons → higher Zeff per remaining $e^{-}$ → smaller size
4	"In isoelectronic series, more electrons = smaller radius"	More charge → contraction	All have same electrons. More protons = greater nuclear pull = smaller radius
5	"Ionic radius always decreases across a period"	Follows atomic radius trend	Comparing differently charged ions across a period is not meaningful without specifying isoelectronic context
6	"Diagonal elements are in the same group"	"Diagonal" sounds like same column	Diagonal relationships (Li-Mg, Be-Al, B-Si) are across different groups AND periods
7	"Noble gases always have negative EGE"	They do accept electrons in some compounds	Noble gases have positive EGE (energy must be supplied to add an electron)
8	"Mendeleev's law is the modern periodic law"	Mendeleev arranged by atomic mass	Moseley (1913) arranged by atomic number — that is the modern periodic law
9	" $O^{2-}$ is smaller than $F^{-}$ because O has fewer protons"	Fewer protons = weaker pull = larger	$O^{2-}$ has 8 protons and 10 electrons; $F^{-}$ has 9 protons and 10 electrons. More protons in $F^{-}$ → smaller. So $O^{2-}$ > $F^{-}$
10	"Groups 2 and 15 have the most negative EGE in their periods"	Trend predicts increasing EGE across period	Groups 2 (filled $ns^{2}$ ) and 15 (half-filled $np^{3}$ ) show less negative or even positive EGE due to subshell stability