The number of $sp^{2}$ hybrid orbitals in a molecule of benzene is

Which one has $sp^2$ hybridisation?

What is the meaning of hybridization of atomic orbitals?

What is the decreasing order of carbon-carbon single bond length in the following compounds?
$(I) CH_2 = CH - C \equiv CH$
$(II) CH \equiv C - C \equiv CH$
$(III) CH_3 - CH = CH_2$
$(IV) CH_2 = CH - CH = CH_2$

What is the proportion of $s$-character in $sp^3$,$sp^2$,and $sp$ hybrid orbitals? What is the order of electronegativity in it?

The hybridisation of $C$ in diamond,graphite and ethyne is in the order