Which carbocation is more stable?

a)sp >sp² >sp³

This is the electronegativity order sp is most electronegative. So ethyne is stronger acid than ethene and ethene is stronger acid than ethane. Hence we can say that ethane is stronger base than ethene and ethene is stronger base than ethyne.

An sp carbon is more electronegative than sp²carbon and sp²carbon is more electronegative than an sp³ carbon, an sp carbon with a positive charge is less stable than sp² carbon with a positive charge and sp² carbon with a positive charge is less stable than an sp³ carbon with a positive charge.

a) spcarbon is more electronegative than an sp² carbon so sp carbon with a positive charge is less stable than an sp² carbon with a positive charge.

b) spcarbon is more electronegative than an sp³ carbon so sp carbon with a positive charge is less stable than an sp³ carbon with a positive charge.