A free radical is an atom or molecule that has an odd number of what?

More Questions:

How many dice are used in a standard game of backgammon?

What is the name of the frog companion that you find in Donkey Kong Country?

Which two books of the New Testament have names that begin with letter "R"?

What literary work inspired Jefferson Airplane's "White Rabbit" song?

What original literary work was the movie "Charly" based on?

What is the largest Japanese island?

What region was explored by Vitus Bering?

Mount Sunflower is what US state's highest point?

In the human body, what is produced by the Islets of Langerhans?

For what does the "T" stand in the name of Star Trek's captain James T. Kirk?

What queen was ordered beheaded by her cousin, Elizabeth I?

What day did the Battle of the Somme end?

Approximately when was the Colosseum built?

What number is represented by "M" in Roman numerals?

What is Shakespeare’s shortest tragedy?