The correct answer is indeed Arsenic (As). This is the element that fits the description of being in period 4 and group 5, just like Krypton and Nitrogen.
Hey there!:
a) Cations which are lowest size generally forms adopts more number of water molecules around it. Such kind of Cations forms largest hydrated ions. Among given cations, Li+ is smallest one and (C4H9)4N+ is largest one. So, Li+ ion forms largest hydrated ion.
b) Organic ligands or alkyl chains contained Cations are hydrophobic in nature due to its low polar nature. Among given (C₄H₉)4N⁺ cation is hydrophobic in nature.
c) Size of cation inversely proportional to the hydrated sphere or number of water molecules attached. So, in the given Cations (C₄H₉)4N⁺ is largest cation which attaches fewest water molecules.
d) Charge on the cation makes it more electrostatic maker. But size is inversily proportional to electrostatic property. (C₄H₉)4N⁺ is electrostatic structure breaker.
e) Al⁺³ has highest charge. So it is most electrostatic structure maker.
Hope this helps!
The correct name of this isotope : Oxygen - 16
<h3>Further explanation</h3>
Given
Isotope : ₈¹⁶O
Required
The correct name
Solution
The elements in nature have several types of isotopes
Isotopes are elements that have the same Atomic Number (Proton)
Atomic mass is the average atomic mass of all its isotopes
In the following element notation,

X = symbol of elemental atom
A = mass number
Z = atomic number
The isotope name is usually followed by its mass number, so the symbol above can be expressed as oxygen - 16