How are eras and periods of the geologic time scale named?

They are named for the places where geologists first described rocks or fossils from that time.
Their names are based on the names of scientists who discovered the rocks and fossils.
They are named after plants and animals that lived during that time.
Their names are based on the number of centuries within that length of time.

For a research project, a student decided to test the effect of the lead(ii) ion (pb2+) on the ability of salmon eggs to hatch. this ion was obtainable from the water‐soluble salt, lead(ii) nitrate, which the student decided to make by the following reaction. pbo(s) + 2 hno3(aq) → pb(no3)2(aq) + h2o losses of product for various reasons were expected, and a yield of 86.0% was expected. in order to have 5.00 g of product at this yield, how many grams of pbo should be reacted? (assume that sufficient nitric acid, hno3, would be used.)