Answer
B. They have a full valence shell.
D. They do not tend to react.
Step-by-step explanation
The noble gases are colorless, odorless, tasteless, and nonflammable nonmetals under standard conditions. They have a full valence shell and because of this they are unreactive and have no shielding layers.
Hence, the true statements of noble gases in the given options are:
B. They have a full valence shell.
D. They do not tend to react.