Which of the following reactions are exothermic?

 

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

In the bond formation of barium with oxygen, the valency electrons from the barium transferred to the oxygen and forms an ionic bond.

One atomic mass unit (AMU) is equal to the one-twelfth the mass of one carbon-12 atom.

Allotropes are the different physical forms of an element. Here in the given options, diamond and graphite are the pair of allotropes of carbon.

Some more examples are Molecular oxygen and ozone are pair of allotropes, Black and red phosphorous are also pairs of allotropes.

Isotopes are atoms of the same element that have different mass numbers.

Example : Hydrogen, Deutirium and tritium all these have different mass but same atomic numbers.

The compound with the molecular formula P4O10 is called Phosphorus pentoxide or tetraphosphorous decoxide. It is an anhydride of the Phosphoric acid.

The unit which is used to measure weighted average atomic mass is Atomic Mass Unit (amu).

The amu or gram/mole can also be used for this measure.

The nucleus of an atom is the densest part of an atom. It contains the protons and neutrons of an atom.

Mixtures are combination of two or more substances physically which can be separated in to the original.

Matter can be breakdown into two categories. 

1) Pure substances 

2) Mixtures

Here in the given options, options A, B, C are pure substances as they are indicated as S & L in brackets. Option D) is an aqueous solution, that can be dissolved in water.