Which of the following reactions are exothermic?

 

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

Because of its being pollution free and  combustion efficient, Hydrogen gas is  called fuel of future. Because of its origin in marshy places, Methane is called as 'Marsh Gas'.

Cutting and Peeling of onion brings Tears to the eyes because of presence of Sulphur in the cell.

Adenosine triphosphate (ATP) is a nucleotide which is also called as nucleoside triphosphate is a small molecule used in cells as a coenzyme. It is often referred to as the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism. Most of the cellular functions need energy in order to be carried out such as synthesis of proteins, synthesis of membranes, movement of the cell, cellular division, transport of various solutes etc. The ATP is the molecule that carries energy to the place where the energy is needed. When ATP breaks into ADP (adenosine diphosphate) and P_i (phosphate), the breakdown of the last covalent link of phosphate liberates energy that is used in reactions where it is needed.

The chemical element with the atomic number 35, Bromine is a non metal that remains liquid at room temperature. Mercury also remains liquid at room temperature but it is a metal. Bromine is the third lightest halogen.