How do scientist know that atoms and molecules combine in well-ordered arrays?

The modern periodic table has groups.

In 1901, thomas edison invented the nickel-iron battery. the following reaction takes place in the battery. fe(s) + 2 nio(oh)(s) + 2 h2o(l) fe(oh)2(s) + 2 ni(oh)2(aq) how many mole of fe(oh)2, is produced when 5.35 mol fe and 7.65 mol nio(oh) react?

Asolution contains 180 g of glucose (c6h12o6) and 162 g of water. what is the mole fraction of glucose?