How can chemists state with certainty that no one will discover an element that would appear on the periodic tabl between sulfur and chlorine

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

Which term refers to a property that depends only on the amount of a substance? ©@

How many liters of hydrogen gas will be produced at stp from the reaction of 7.179×10^23 atoms of magnesium with 54.219g of phosphoric acid (h3po4) the equation is 3mg + 2h3(> mg(po4)2+3h2