Confusion in comparing the contribution of resonating structures to resonance hybrid [closed]

Question

So I was comparing the $+M$ effect of $\ce{-CH^-_2}$, $\ce{-NH^-}$ and $\ce{-O^-}$. Answer was given as:

$$ \ce{-CH^-2 > -NH^- > -O^-}$$

So, I attach them with ethene and made their respective resonating structures as: $\require{enclose}$

1. $\ce{\underset{(a)}{CH2=CH-\overset{\ominus}{C}H2} <-> \underset{(b)}{\overset{\ominus}{C}H2-CH=CH2}}$

2. $\ce{\underset{(a')}{CH2=CH-\overset{\ominus}{N}H} <-> \underset{(b')}{\overset{\ominus}{C}H2-CH=NH}}$

3. $\ce{\underset{(a'')}{CH2=CH-\overset{\ominus}{O}} <-> \underset{(b'')}{\overset{\ominus}{C}H2-CH=O}}$

So my doubt was whether $b$, $b'$ and $b''$ have same contribution to their respective resonance hybrid or it's different ?

Or it's that they have same relative contribution but order of $+M$ is determined by inductive effect in resonating structures or inductive effect determines resonating structure contribution ?

Answer 1

For $b$, you have equivalent resonating structures as the structures are identical.

The structures $a'$ and $b'$ are not correct as nitrogen cannot expand it's octet.

For $a''$ and $b''$, the first structure $(a'')$ is more stable as there is negative charge localised on electronegative atom as compared to $b''$ where it is localised on carbon.

For the second question, I think inductive effect is completely different than the mesomeric effect. For determining the order of the strength of mesomeric effect, you can simply compare their electronegativity orders, more is the electronegativity, lesser is the strength to donate electrons.