An atom hopefully this helps
Answer:

Explanation:
Oxygen has eight eletrons and six valence electrons, giving it the electron configuration of
.
Answer:Atomic theory established that all matter is made of tiny particles, a discovery that led to amazing scientific breakthroughs in areas from modern chemistry to nuclear energy.
Explanation:Atomic theory is the scientific theory that matter is composed of particles called atoms. Atomic theory traces its origins to an ancient philosophical tradition known as atomism.
Potassium outermost electron occupy "4s" orbital
Answer:
Percentage by mass of oxygen = 76.20% (Approx)
Explanation:
Given:
HNO3
H=1, N=14, O=16]
Find:
Percentage by mass of oxygen
Computation:
HNO3
Total mass = 1 + 14 + 3(16)
Total mass = 63
Mass of oxygen = (3)(16) = 48
Percentage by mass of oxygen = [48/63]100
Percentage by mass of oxygen = 76.20% (Approx)