Which element has an equal number of electron pairs and of unpaired electrons within orbitals of principal quantum number 2?

The footprints of a dinosaur and the burrow of an ancient shrimp are examples of which kind of fossils

At which temperature would a reaction with ah= -220 kj/mol and as=-0.05 kj/(mol-k) be spontaneous?

Which of the following involves only abiotic factors? a. a large rock being weathered by wind and rain b. an otter using a stone to break open a sea urchin c. a spider building a web in the corner of a building d. a pine tree absorbing light from the sun