Is it possible to do a NULL comparison in Relational Algebra?

Question

Please consider the following question given in a booklet:

I have read about databases from Database System Concepts - by Henry F. Korth, but never saw an instance where we could do a NULL comparison in relational algebra queries - unlike SQL queries.

(C) is given the correct option, but my question is:

Is the statement III given above, a valid Relational Algebra query?