A first order reaction initially contains 1. 00 × 10²⁰ molecules. If the reaction has a half-life of 20. 0 minutes, how many molecules remain unreacted after 80. 0 minutes?.

In the image, layer a is the topmost layer. layer c contains fossils from the precambrian era. layer b contains dinosaur fossils, and layer a contains fossils of mammals. which two statements are supported by this evidence? 1. mammals lived before the precambrian era. 2. dinosaurs and mammals existed in the precambrian era. 3. dinosaurs evolved after precambrian organisms. 4. precambrian organisms evolved after dinosaurs. 5. precambrian organisms were the first life-forms to become fossilized, according to this sample.

If your not fit to drive you have a responsibility to

When do you think it’s best to take the psat (what grade year / when in the year)?