Which of the following is a linear molecule?

In $XeF_2$,the hybridisation of $Xe$ is:

Predict the hybridization of each carbon in the molecule of the organic compound given below. Also,indicate the total number of sigma $(\sigma)$ and pi $(\pi)$ bonds in this molecule.
$HC \equiv C-CO-CH_2-COOH$

Which of the following has been arranged in increasing order of size of the hybrid orbitals?

Which species do not have $sp^3$ hybridization?

What is the structure of $CH_2 = C = CH_2$?