Multiply h20, the formula with an odd number of oxygen atoms, by the smallest number which will make an even number of oxygen atoms

The number is 2.

Explanation: The molecular formula of water is . It contains two atoms of hydrogen and one atom of oxygen.

Thus there is an odd number of oxygen atom. To make the atoms even , with the smallest number, we multiply the formula by 2. The number of oxygen atoms in 2 will be 2 , which is an even number.

1.solid

2.carbon dioxide

3.helium

they it depends on if one believes about radioactivity, they make a geiger counter beep but maybe it was going to beep anyway electronics do wierd things all the time or it was programmed to beep near certain metals.