Gas hydrates are compact chemical structures made of natural gas and
a. halite.
b. water.
c. manganese.
d. petroleum.

                  Option-B (water) is the correct answer.

Explanation:

                 Gas hydrates are made up of Solid-Ice water and a natural gas like Methane gas trapped in the lattice of ice water. Gas hydrates are mainly found deep down in the sea where the atmospheric pressure is greater than 1 atm.

Generally Gas hydrates have two main applications. 

                             a) It stabilizes the sea floor other wise its melting will cause land sliding in sea floor. 

                             b) Secondly, it traps a green house gases like Methane, if released these gases could produce Climate changes.

hey there!

mass = 6.75 g

volume =   9 cm³

therefore:

d = mass / volume

d   = 6.75 / 9

d = 0.7 g/cm³

answer b