Which of the following reactions are exothermic?

 

$$\begin{gathered} 1) C + O2 → CO2 \\ 2) 2Mg + O2 → 2MgO \\ 3) CuSO4 + 5H2O → CuSO4.5H2O \\ 4) All the above \end{gathered}$$

The boiling point of the compounds depend on the number of carbons in them. Hexane has 6, Pentane has 5 and Propane has 3 carbons. As Hexane is with 6 carbons it has highest boiling point and next Pentane with 5 and lowest Propane with 3. 

The chemical composition of a rock is mainly minerals.

Br-Br.

In Br2, two of the same atoms, pull on each side of the bond is equal making it as non-polar.

The other options all include a significantly more electronegative atom (the oxygens and the chlorine), so those bonds are all polar covalent.

In this chemical reaction chlorine change oxidation number from 0 to -1 (reduction) and bromine change oxidation number from -1 to 0 (oxidation).

Chlorine is stronger oxidation reagent than bromine.

In VIIA or group 17 (halogen elements) there are six elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At) and tennessin(Ts).

They have high electronegativity because they have seven valence electrons in their outermost energy level, so they can gain an electron to have the octet rule.  

Going down in the group, element are weaker oxidazing reagent and less reactive.

The two elements that are used to make bronze are tin and lead.