Threatened is the definition used when describing a species at risk of extinction
Where organisms are better adapted to their environments tend to survive and produce more kids!
No 6 is common for N and H. 3 is only for H(Hydrogen).
For finding the number of hydrogen atoms we should multiply 6 with 3
So, 6*3 = 18. So there will be 18 hydrogen atoms in 6NH₃
A liquid can not be a crystalline