Anton van Leeuwenhoek used a microscope to observe tiny creatures swimming in a drop of pond water.
How did his observations contribute to the cell theory?
A. He showed that living cells come from other living cells.
B. He was the first person to observe and identify living cells.
C. He was the first person to observe dead plant cells.
D. He showed that all plants and animals are made of cells.

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

Which statement is true about hcl? (5 points) select one: a. it is a salt because it increases the concentration of metallic ions. b. it is a salt because it is formed by the reaction of an acid and a base. c. it is an acid because it increases the concentration of hydroxyl ions. d. it is an acid because it increases the concentration of hydronium ions.

Modern pennies are composed of zinc coated with copper. a student determines the mass of a penny to be 2.482 g and then makes several scratches in the copper coaling (to expose the underlying zinc). the student puts the scratched penny in hydrochloric acid, where the following reaction occurs between the zinc and the hcl (the copper remains undissolved): zn(s) + 2 hcl(aq) → h2(g) + zncl(aq)the student collects the hydrogen produced over water at 25 °c. the collected gas occupies a volume of 0.899 l at a total pressure of 79 j mmhg. calculate the percent zinc (by mass) in the penny. (assume that all the zn in the penny dissolves.)