If every oxygen ion (combined with an aluminum ion) has a charge of –2, what must the charge of each aluminum ion be? how can you tell this? also, what has to happen to an uncharged aluminum atom so that it will bond with oxygen?

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.

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.