The correct answer is:
Metals
They are all alkali and transition metals
Explanation:
The periodic table includes elements clustered into groups with comparable properties. Alkali metals are reactive, soft metals with low densities. Transition metals are unreactive metals that have many have common uses. Halogens are reactive non-metals that form glowing vapors.
I guess you are asking what world should go at the beginning of the sentence. If I am right, it is energy.
When HCl reacts with a metal, hydrogen gas will be evolved. To test this gas, insert a burning splinter into the outlet of gas, the flame will be extinguished with a pop sound. This will confirm the gas is hydrogen.
Answer:
6
Explanation:
There is 2 of the coumpond, in one compound, there are 3 oxygens. But when there are two, it is 6.