all the elements in group 1 react with water to form a hydroxide. what other substance is also produced?

The other substance produced is hydrogen gas.

Key idea

When a Group 1 metal (like lithium, sodium or potassium) reacts with water, the word equation is:
metal + water → metal hydroxide + hydrogen (gas).

Example equation

For sodium, the balanced symbol equation is:
2Na + 2H₂O → 2NaOH + H₂.

So alongside the metal hydroxide solution, bubbles of hydrogen gas are released.

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