A) explain why caesium is more reactive than potassium. b) Write the formula of
i) caesium nitrate
ii) caesium sulphate​

Explanation:

(a) Firstly, caesium abd potassium are both in Group 1 of the periodic table. Group 1 metals (also called alkali metals) are the most reactive metals of the periodic table. Caesium is more reactive than Potassium because it has a higher electropositivity than Potassium. Electropositivity is the tendency of a metal to donate electron(s) to form a cation. Electropositivity increases down the group; this is because it is easier for atoms to loose electrons on the outermost shell that are far away from the central nucleus as against atoms whose outermost electrons are closer to the central nucleus. Thus, the more "bulky" an atom is, the farther it's outermost electrons (valence electrons) get from the central nucleus and the easier it is to lose the outermost electron(s). And the easier it is for the valence electron(s) to be removed, the more reactive the atom would be and vice-versa.

Caesium is more reactive than potassium because it is more bulky than potassium, with an atomic number of 55, while potassium has an atomic number of 19.  

NOTE: The closer an electron is to the nucleus, the more difficult it is to be removed from it's shell.

(b) i. Formula for Caesium Nitrate:

Symbol for Caesium is Cs and Nitrate is NO₃⁻.

Cs⁺ + NO₃⁻  ↔  CsNO₃

Formula for Caesium Nitrate is  CsNO₃

ii. Formula for Caesium sulphate

Symbol for caesium is Cs and Sulphate is SO₄²⁻

Cs⁺ + SO₄²⁻  ↔   Cs₂SO₄  

Formula for Caesium sulphate is Cs₂SO₄

NOTE: When writing the formulae, the charges would be exchanged to form the subscript as seen on the product sides above.