In the reversible reaction in water solution nh3 + h2o ⇀↽ nh+ 4 + oh− , what acts as a bronsted-lowry acid and what acts as a bronsted-lowry base? 1. oh−; h2o 2. h2o; oh− 3. h2o; nh+ 4 4. oh−; nh+ 4 5. nh3; h2o

The equation is:
NH₃     + H₂O     ↔    NH₄⁺          +       OH⁻
base       acid            conj. acid        conj. base

NH₃ is the proton acceptor so it considered as Bronsted-Lowry base and H₂O is proton donor so it considered as Bronsted-Lowry acid 

NH₃ when accepted H⁺ it converted into NH₄⁺ (conjugate acid) and H₂O when losing H⁺ it converted into OH⁻ (conjugate base)

The question asks for acid and base 
1) OH⁻ base, H₂O acid
2) H₂O acid, OH⁻ base
3) H₂O acid , NH₄⁺ acid
4) OH⁻ base, NH₄⁺ acid
5) NH₃ base, H₂O acid

so the correct answer is 2) because it is the only one containing acid then base

Not a  mixture of two common elements that can be separated by physical means.