The correct statement about probability density (except at infinite distance from nucleus) is :

Probality density changes with distance (radius) from nucleus. It becomes zero at radial nodes.

In 2s graph, the probability density curve becomes zero at a point which is know as node. Hence, potion (a) is wrong.

Probability density is the square of wave function and hence is always positive . So, option (b) is wrong.

In 3p graph, we have a minimum curve which denotes the node where probability density is zero. Hence, option (C) is the correct statement.

In 1s graph, the probability density curve does not become zero at any distance hence, option (d) is wrong.