An unknown gas is likely to be carbon dioxide if it has which of the following
characteristics?
a
turns limewater milky
b. is flammable
c. is less dense than air
d. has a penetrating odor

An unknown gas is likely to be carbon dioxide if it turns limewater milky.

Option a

Calcium Hydroxide also known as lime is a sparingly soluble compound which when dissolved in water produces an alkaline solution known as lime water. When a gas such as carbon dioxide passes through this alkaline solution, it turns lime water milky due to the formation of an insoluble suspension of calcium carbonate . This can be understood by the following chemical reaction-

If an excess amount of gas is added in the solution, the following reaction takes place:

At this stage, the milkiness of the solution disappears since "calcium bicarbonate is soluble in water".

for points guys

it would be a gas formation