A guy on a bike goes 400m north, turns around and goes
200m south. It takes 60
seconds to make the trip. What
s his distance, displacement and
average speed?

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

b. accuracy of the data matters alot more than its number of digits, organization or amount of detail. quantitative observation is more accepted than the qualitative observation.