Alkanes Alkenes And Alkynes Conformations And Hybridisation

In the given hydrocarbon, 

The type/state of hybridization of carbons 1, 3, and 5 respectively are:

1. sp², sp, sp³

2. sp, sp³, sp²

3. sp, sp², sp³

4. sp³, sp², sp

The molecule among the following that has the hybridization ${\mathrm{sp}}^2,\hspace{0.17em}{\mathrm{sp}}^2,\hspace{0.17em}\mathrm{sp},\; and\hspace{0.17em}\mathrm{sp}$ from left to right atoms is:

1. $\mathrm{HC}\equiv \mathrm{C}-\mathrm{C}\equiv \mathrm{H}$

2. ${\mathrm{CH}}_2=\mathrm{CH}-\mathrm{C}\equiv \mathrm{CH}$

3. ${\mathrm{CH}}_2=\mathrm{CH}-\mathrm{CH}={\mathrm{CH}}_2$

4. ${\mathrm{CH}}_2-\mathrm{CH}=\mathrm{CH}-{\mathrm{CH}}_3$

The dihedral angle of the least stable conformer of ethane is: