The easiest way to find out if a physical science text book has an answer key is to visit the publisher's website. Most publishers have online resources for each of the textbooks listed there.
Pearson Prentice Hall has online resources for its physical science textbooks; however, it does not offer an answer key. McGraw-Hill offers textbook access through a paid service called Connect. It provides access to textbook questions with answers, as well as other study resources. Connect is available free for 14 days as a trial before the customer buys.
Students may also be able to find answer keys on textbook rental websites. Some rental websites provide access to answer keys at an additional cost, or they may be thrown in as a free extra.