$($c$)$ State what will happen :

$($i$)$ Dislocation avoids obstacles

$($ii$)$ Unlike edge dislocations move closer on the same slip plane.

$($iii$)$ Two screw dislocations intersect

$($iv$)$ Poles are lying on the same longitude

$($d$)$ Calculate the lattice parameter of a BCC crystal whose atomic radius is $0\mathrm{.}286$ nm $.$