[SOLVED] Graph operations ??

can someone help me with this plz? there are 2 questions.

1.

A graph is defined as a pair of 2 sets. therefore operations on graphs are defined in terms of sets and set operations. Define the following operations on graph.

1. union

2. intersection

3. compliment

4. decomposition

2.

in set theory we have empty set what is the analogues concept in empty set of graph theory. Find different concept for empty graph and determine the situations where each definition is suitable.