Van der waals forces are very strongly repulsive to each other at long nuclear distances very strongly attractive to each other at long nuclear distances very strongly repulsive to each other at short nuclear distances very strongly attractive to each other at short nuclear distances

Very strongly repulsive to each other at short nuclear distances

Explanation:

Van der wall forces are weak intermolecular forces that may be either attractive or repulsive. Generally these forces are attractive in nature. But as the distance between the atoms are reduced to less than 5 nm. The nucleus of the atoms are close enough to repel each other(because of like charges). Hence, when atoms are at short distances they repel each other.

So, here the third option is correct that is Very strongly repulsive to each other at short nuclear distances

d) physical means can be used to separate the components of air.

this could be newton#'s law of cooling. the cooling curve is exponential