Answer:
D. MgO
Explanation:
We need to look at the charge of element. (Look at a periodic table for this)
Mg, which is Magnesium, has a charge of 2+ because it's in the second column, or group, from the left.
O, which is Oxygen, has a charge of 2- because it's in the second column, or group, from the right.
Since Mg is 2+, it's the cation and since O is 2-, it's the anion. We can put these two elements together into an ionic compound.
Mg^(2+) and O^(2-) becomes Mg2O2, where we can cancel the 2s: MgO.
Thus, the answer is D.
Hope this helps!
Ch3ch2ch2ch2ch2ch3 Is called Hexane, it is a colorless liquid hydrocarbon
Answer: 
Explanation:
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 iron is having an oxidation state of +3 called as
cation and oxide
is an anion with oxidation state of -2. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral
.
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.

Explanation:
Atomic size is defined as the distance between the nucleus and valence shell of an atom. Valence shell is the outermost shell of an atom.
When we move across a period in a periodic table then there will occur a decrease in atomic size of the atoms. But when we move across a group in a periodic table then there will occur an increase in atomic size of the atom.
Hydrogen is a period 1 element, oxygen is a period 2 element, chlorine is a period 3 element and bromine is a period 4 element.
Therefore, given elements are arranged in order of increasing atomic size as follows.
H < O < Cl < Br