Which of the following is associated with Torsional strain?

In the given conformation, ${\mathrm{C}}_2$ is rotated about ${\mathrm{C}}_2-{\mathrm{C}}_3$ bond anticlockwise by an angle of $120°$. Then, the conformation obtained is:

The pair of the structures given below represent:

In the following structures, which two forms are the staggered conformation of ethane?

(1) 

(2) 

(3) 

(4) 

The structures $\mathrm{I} \text{and} \mathrm{II}$are:

Incorrect statement about the compounds $\mathrm{I}, \mathrm{II}$ is

$\left(\mathrm{I}\right)$ 

$\left(\mathrm{II}\right)$ 

$\left(\mathrm{III}\right)$