Answer:
BaCl₂ and H₂SO₄
Explanation:
The reaction is the precipitation of BaSO₄ from solution.
This means that our reactants must contain the Ba ion and SO₄²⁻ ion. The reactants that meet this criteria are the; BaCl₂ aand H₂SO₄
The reaction is given as;
BaCl₂ + H₂SO₄ --> BaSO₄ + 2HCl
<u>Answer:</u> Non-metals form ions when they gain electrons.
<u>Explanation:</u>
An ion is formed when an atom looses or gains electron.
- When an atom looses electrons, it will form a positive ion known as cation.
- When an atom gains electrons, it will form a negative ion known as anion.
Metals are the elements which have a tendency to loose electrons and thus they form cations. <u>Example:</u> Sodium will loose 1 electron to form 
ion.
Non-metals are the elements which have a tendency to gain electrons and thus they form anions. <u>Example:</u> Fluorine will gain 1 electron to form 
ion.
Hence, non-metals form ions when they gain electrons.
An atom is most stable when it has eight electrons in its outermost energy level.
Answer is: hydrogen bonds.
Hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen atom (H), covalently bound to a highly electronegative atom such as flourine (F), oxygen (O) and nitrogen (N) atoms.
According to the principle of base pairing hydrogen bonds could form between adenine and thymine (two hydrogen bonds between this nucleobases) and guanine and cytosine (three hydrogen bonds between this nucleobases).
Adenine and guanine are purine derivatives and thymine and cytosine are pyrimidine derivates.
