Decision Tree - Can the Entropy of a Node be Zero?

Question

The formula for information gain is give by,

Information Gain = entropy(parent) – [average entropy(children)]

Can the entropy be zero, which means in some case:

entropy(parent) == [average entropy(children)]

Answer 1

"When H(S) = 0, the set S is perfectly classified (i.e. all elements in S are of the same class)." -- https://en.wikipedia.org/wiki/ID3_algorithm

H(S) = entropy ;)