1.(a) What is the difference between efflorescence and deliquescence?
  (b) What is pH scale? How can you know if the given sample is acidic, basic or neutral from its pH value?
  (c) Give chemical name formulas and one use of POP.
2. (a) Write the chemical equation for the production of washing soda from soda ash.
    (b) Explain the Chlor-alkali process with chemical equations.
    (c) Explain two uses of baking soda along with reactions.

Hint: It is formed as mineral-rich water rises to the surface through capillary action and then evaporates. Sodium carbonate is an inorganic chemical compound. Sodium carbonate is what is commonly known as Soda ash.

Complete step by step solution:
(a) Deliquescent substances are solids that can get dissolved by absorbing water vapor. But this absorption depends on the humidity of the environment. Efflorescent substances are crystals that can lose water molecules that are already present in their molecular structure.

(b) The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14.A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times more alkaline (another way to say basic) than the next lower whole value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8.

(c) The chemical name of plaster of Paris (POP) is calcium sulphate hemihydrate because half-molecule of water is attached with calcium sulphate. The chemical formula of plaster of Paris is $CaS{O_4}.\dfrac{1}{2} {H_2}O$.
Uses: It is light in weight and more durable. It has low thermal conductivity. It is very good fire resistant and hence a very good heat insulating material.

(a) Washing Soda is sodium carbonate containing 10 molecules of water of crystallisation. So, we can say that washing soda is sodium carbonate decahydrate ($N{a_2}C{O_3}.10{H_2}O$).
 Anhydrous sodium carbonate or soda ash is dissolved in water and recrystallised to get washing soda crystals containing 10 molecules of water of crystallization. $N{a_2}C{O_3} + 10{H_2}O \to N{a_2}C{O_3}.10{H_2}O$

(b) It is a type of decomposition reaction. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is called the chlor-alkali process because of the products formed- chlor for chlorine and alkali for sodium hydroxide. Following is the chemical equation for the process $2NaCl + 2{H_2}O \to 2NaOH + C{l_2} + {H_2}$
 Chlorine gas is liberated at the anode while hydrogen gas is liberated at the cathode.

(c) Baking soda is the common name of sodium bicarbonate. The chemical formula of baking soda is $NaHC{O_3}$. It Reduces the acidity in the stomach, acts as an antacid which is used to treat stomach upset and indigestion and used in the process of washing as a water softener.

Note: Efflorescence usually consists of gypsum, salt, or calcite. Deliquescence, the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. Washing soda and soda ash are both sodium carbonate. Washing soda contains a lot more water than soda ash does, although it too is a dry white powder