In the city a street peddler offers you a diamond ring for 30 bucks how can you test the rock

Explanation:

Hardness test — Scratch the rock with a fingernail, a copper penny, a glass plate or nail, and a ceramic plate. Check your Guide to assign it a rating on the Mohs Scale of Hardness.

Color streak test — Test for the “color streak” of the minerals by rubbing the rock across the ceramic plate in the Mineral Test Kit, or across smooth

cement. Look up which colors indicate which minerals are present.

Magnetism test — Hold the magnet in the Mineral Test Kit near your rock. If there is a magnetic pull, it has a metal mineral in it.

Acidity test — Put vinegar in the bottle included in the Mineral Test Kit. Squeeze out a few drops on the rock. If it fizzes, it contains carbonate.

A quick and easy way to find out whether your diamond is real or fake: try fogging it up with your breath. If it clears up after one or two seconds, then your diamond is real, but if it stays fogged for three to four seconds chances are that you're looking at a fake.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

the answer would be c