Answer:
A
Explanation The number of energy levels (n) increases, and so does the distance between the nucleus and the outermost orbital. The increased distance and the increased shielding weaken the nuclear attraction, and so an atom can't attract electrons as strongly.
Answer: An electron having a quantum number of one is closer to the nucleus
Explanation:
The Bohr model relies on electrostatic attraction between the nucleus and orbital electron. Hence, the closer an electron is to the nucleus the more closely it is held by the nucleus and the lesser its energy (the more stable the electron is and the more difficult it is to ionize it). The farther an electron is from the nucleus ( in higher shells or energy levels), the less the electrostatic attraction of such electron to the nucleus due to shielding effect. Hence it is less tightly held.
Answer: The coefficient for 
is 12.
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.
Thus in the reactants, there are 12 molecules of oxygen in balanced chemical equation. Thus the coefficient for is 12.
