Which of the following reactions are exothermic?

 

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

Cathode rays made of beams of electrons.

Washing soda is the common name for Sodium Carbonate (Na2CO3). It is also called as Soda Ash.

Talc or talcum is a clay mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 is the main ingredient in face powders that absorbs moisture and oil.

It is also called as French Chalk. Other ingredients include Calcium carbonate (chalk), Magnesium carbonate, China clay, starches like rice and potato, zinc oxide,...

Anaerobic glycolysis is the transformation of glucose to lactate when limited amounts of oxygen (O2) are available. 

Hence, Anaerobic glycolysis occurs without oxygen.

A half reaction is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction.

Covalent bonding occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability.

Examples of compounds with covalent bonds ::

HCl, CO2, O2,... 

Yes, all the given statements are NOT true about electrons and atomic orbitals.

True statements are ::

An orbital can contain a maximum of two electrons.

An atom’s lowest energy level has only one orbital.

An electron has different amount of energies in all orbitals.