How many isomers with the sum formula C7H16 can be isolated in pure form?

This is the question from our lecture about Chirality and Stereoisomers. It refers to the page with configurational isomers. But I don't understand what is meant by pure form. I know C7H16 has nine isomers. Are they asking me to determine the chiral centres of each of these nine isomers of C7H16?