Which of the following reactions are exothermic?

 

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

Water can moderate temperature because of the two properties: high-specific heat and the high heat of vaporization. 

Hence, all the above given options are not the properties of water.

In chemistry, Weak bonds are those forces of attraction that, do not take a large amount of energy to break.

For example, hydrogen bonds are broken by energies in the order of 4 - 5 kcal/mol.

Ionic bonds, hydrogen bonds and van der Waals interactions are considered weak bonds.

Weak bonds are transient and easily reversible.

Bond breaking is an endothermic process.

Hence, bond breakage needs an amount of energy and uses some energy based on the strength of the bond to break the bond.

Copper Iodide is the systematic name of the given compound (CuI)s.

The relationship between a cathode and an anode involves the transfer of electric charge between them. The cathode is the negative terminal on the battery, which has zero electric potential. The anode is the positive terminal on the battery and has the battery's maximum electric potential. Current flows from the battery's anode (positive terminal) to the cathode (negative terminal). In electron flow, electrons leave the negative side of the battery and move towards the positive side of the battery.

Hence, The relationship between a cathode and an anode involves Electrons.

The given statement is True.

Ketchup is acidic, having a pH of 3.9. The acidic component, acetic acid, will react with the metal tin. This reaction will result in a metal acetate that will contaminate the ketchup.

Hence, The acetic acid in the ketchup will react with the metal tin, forming a metal acetate that will pass into the ketchup which leads to its contamination.

The systematic name for a chemical is the unique name given to it by the International Union of Pure Applied Chemistry (IUPAC). The IUPAC name can differ from a chemical compound's general name.

PbO is an ionic compound since it consists of a Lead as metal and Oxygen as nonmetal. The systematic name for PbO is Lead (II) oxide. Here we need to put the (II) since lead has more than one combining capacity.