Which of the following has an unstable enol form?

The orbital picture of a singlet carbene $(:CH_2)$ can be drawn as:

Which of the following intermediates has a complete octet around the carbon atom?

Which free radical structure will show the maximum resonance? (Given: $\phi = C_6H_5$)

Consider the following compounds:
$(I)$ $(CH_3)_3C-CH^{\bullet}-C_6H_5$
$(II)$ $(C_6H_5)_3C^{\bullet}$
$(III)$ $2$-methylbicyclo$[2.2.1]$hept$-2-$yl radical (as shown in the image)
Hyperconjugation occurs in:

Arrange the following carbocations in decreasing order of stability:
$I: CH_3-CH_2^+$
$II: (CH_3)_2CH^+$
$III: Ph-CH_2^+$