Pls help me with this question thank you

Match term definition ellipse a) diagonal cross section of a cylinder circle b) diagonal cross section through the widest part of a sphere sphere c) cross section parallel to the base of a cone great circle d) shape created when a semi-circle is rotated around the y-axis triangle e) perpendicular cross section of a cone

What type of matter is made of only one kind of atom

Which factor is likely to impact the possible number of compounds ?