Misc: What is the more common name of nitrous oxide?

Questions

The city of --------- used to be known as Puerto Rico (which means "rich port" in Spanish), while the island of Puerto Rico was originally named San Juan.?

The water of the ----------- is seven to eight times saltier than ocean water.?

The white cliffs of ---------- is a natural landmark located at the southern coast of England. The distinctive color of the cliffs was actually created by the accumulation of skeletal remains of tiny organisms deposited over thousands of centuries. Sea level was higher millions of years ago, and after the waters receded, the whitish residual remains of the creatures were exposed.?

The --------------- is not a sea, but a landlocked salt lake, 45 miles long by 9 miles wide.?

The world's biggest meteor crater is located in New Quebec, --------------?