Student B because it requires a hypothesis
Nuclear fission is the process of which a large nucleus splits into two smaller nuclei with the release of energy and neutron. In simpler words, nuclear fission is the process in which a nucleus is split into two smaller fragments or pieces (nuclei) and so energy and neutrons are released. The resulting pieces of this fission process have less combined mass than the original piece (nucleus) and the missing was is converted into nuclear energy.
Answer: 
incorporates both ionic bonding and covalent bonding.
Explanation:
A covalent bond is formed when an element shares its valence electron with another element. This bond is formed between two non metals.
An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and the element which accepts the electrons is known as electronegative element. This bond is formed between a metal and an non-metal.
For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.
Here potassium is having an oxidation state of +1 called as 
cation and nitrate 
is an anion with oxidation state of -1. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral .
is formed by sharing of electrons between two non metals nitrogen and oxygen.
Thus incorporates both ionic bonding and covalent bonding.
Answer:
En el caso del sodio, la valencia es 1, ya que tiene un solo electrón de valencia, si pierde un electrón se queda con el último nivel completo.
Explanation:
Grupo de la tabla periódica Electrones de valencia
Grupo 14 (IV) (Grupo del carbono) 4
Grupo 15 (V) (Grupo del nitrógeno ) 5
