A science teacher set up a fish tank in her classroom to bring science to life. While cleaning the fish tank, a small piece of a plant broke away from the stem and floated upward and in the opposite direction of the heater. Upon reaching the opposite end of the tank, the plant piece gradually sank. It then floated back to the heater, where it rose once again. This movement repeated until the plant piece was removed from the fish tank. As water cools, it becomes more dense. As water reached the surface of the tank, it became cooler and began to sink. As the water sank, it heated again and moved upward again.
The plant piece cycled around the tank with the moving water. This cycling of cool and warm water is an example of
A. convection.
B. conduction.
C. expansion.
D. radiation.

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.

the answer is c.the valence of the atoms combine .