You are working in a lab and find that you need to make a 0.5 M solution of hydrochloric acid (HCI). You have available to you a 12 M stock solution
and 100 mL volumetric flasks. What volume of the stock solution do you
need to use to make this 0.5 M solution given the available equipment and
chemicals?

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

because natural gas is colorless, odorless, and tasteless, distributors add mercaptan (a chemical that smells like sulfur) to give natural gas a distinct unpleasant odor (it smells like rotten eggs). they locate the types of rock that are likely to contain natural gas deposits.