Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!

The main cations found in living beings
are the [?] cation (Na+), the
[?] cation (K+), the calcium
cation (Ca++), the iron cations (Fe
++,Fe+++), the [?] cation (Mg
++),the cation (Zn++) and the
cation (Mn++).