Does the electrolysis of water make mass disappear?

Which of the following elements is a representative element? a. chromium (cr) b. aluminum (al) c. mercury (hg) d. silver (ag)

Calcium hydride (cah2) reacts with water to form hydrogen gas: cah2(s) + 2h2o(l) → ca(oh)2(aq) + 2h2(g) how many grams of cah2 are needed to generate 45.0 l of h2 gas at a pressure of 0.995 atm and a temperature of 32 °c?

In this chemical reaction, 325 grams of barium (ba) react completely. how many moles of lithium (li) are produced?