#### Answer

All but $_{18}^{9}X$ are isotopes of X.

#### Work Step by Step

Since the element has an atomic number of 9, all species with an atomic number of 9 are X's isotopes, so all but $_{18}^{9}X$ are isotopes of X.

Published by
Cengage Learning

ISBN 10:
1133949649

ISBN 13:
978-1-13394-964-0

All but $_{18}^{9}X$ are isotopes of X.

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