What is the increasing order of stability of carbon ions with the change in hybridization of carbon?

Which one amongst the following possesses an $sp$ hybridized carbon in its structure?

The hybridisation of each carbon in the following compound respectively is:
$CH_3-C(=O)-CH_2-CN$

What is the hybridization state of carbon atoms $1, 2, 3,$ and $4$ in the given reaction?

The ascending acidity order of the following $H$ atoms is:
$A: HC \equiv C-H$
$B: H_2C=CH-H$
$C: (CH_3)_3C-H$
$D: CH_3-CH_2-H$

Consider a positively charged $C_2H_3$ species in which the positively charged carbon is $sp$-hybridized,the uncharged carbon is $sp^2$-hybridized and an empty $p$-orbital is perpendicular to the $\pi$ system. What is the best description of this cation?