You can buy them from Citadel Souvenirs.
You can look for pets at shops on Illium and the Citadel.
If you mean the "800 blocks" on the Citadel, then yes, you will go there as part of a mission.
After beating the Citadel, go to the Artemis Tau cluster to look for Liara T'soni, and you'll get her.
It will not affect the mass in any way whatsoever.
Temperature can affect the mass of something and also freezing the object.
For me i saw three endings. You go up and the catalyst offers you three options. (You die in all of these endings. This is the end of the trilogy after all),Option 1: Destroy all synthtic life. You take out your pistol and shoot the power conduit untill it explodes. The citadel fires a red shockwave that destroys all the reapers and mass relays. The citadel is destroyed. Option 2: Control all synthetic life. Put your hands on two energy coils that vaporizes you and the citadel sends out a blue shockwave. The reapers on earth turn blue and fly away. The mass relays are again destroyed. The citadel however closes up. Option 3: Synthesize organics and synthetics. You step in a beam and you are absorbed into the citadel. The citadel fires a green shockwave that makes the reapers fly away and makes the mass relays explode. The citadel is destroyed. At the end of all of these the normandy crashes on aplanet and all of you surviving sqaudmates step out. The game ends. However at the end of synthesis you can see the green leaves tinged with the metallic blue tinge of synthetic. Then the game fades to black. Hoped that helped. Might be more endings.
One of the factors that affect mass communication is poor infrastructure. Lack of knowledge and poverty also affect mass communication in Tanzania.
No because mass doesn't means how it affect far it rolls
No.
No, mass remains constant.
no and mass is air