Question

In a test tube, add red cabbage juice and some lemon juice, the violet colour of red cabbage turns to --.
A.Red
B.Blue
C.Black
D.No colour change

Answer 1

Hint:Acids: Those compounds or solutions which can give hydronium ion or proton donor or electron pair acceptors and have pH range $0-7$, are known as acids.
Bases: Those compounds or solutions which are proton acceptor, can accept hydrogen ion or give hydroxide ion, or electron pair donor and have pH range $7-14$, are known as bases.

Complete step by step answer:
First of all we will discuss acids, bases and amphoteric compounds.
Acids: Those compounds which on ionization produce $$H^{+}$$ ions, are known as acids. They are sour in taste. Acids change the color of litmus from blue to red. When they react with bases then they become less acidic.
Bases: Those compounds which on ionization produce $O{H}^{-}$ions, are known as bases. They are slippery in nature. Bases change the color of litmus from red to blue. When they react with acids then they become less basic.
Generally red cabbage juice is of violet color and when it comes in contact with any acid then its color changes to red and when it comes in contact with bases then its color changes to either green or yellow. So when we add red cabbage juice and some lemon juice, the violet colour of red cabbage turns to red because lemon juice is acidic in nature.

Hence option A is correct.

Additional information:
There are so many factors by which we can decide whether a compound or solution is acidic or basic.
pH values: If the pH value is in between $0-7$ then the solution or compound will be acidic in nature and If the pH value is in between $7-14$ then the solution or compound will be basic in nature. And if the pH value is exactly seven then compound or solution will be neutral i.e. neither acidic nor basic in nature.
Electron pair acceptor and donor: This concept was given by Lewis. According to Lewis: Lewis acids are those substances or solutions which can accept electron pairs and Lewis bases are those substances or solutions which can donate electron pairs.
Arrhenius concept: According to Arrhenius: Acids are those compounds or solutions which can give hydrogen ion or hydronium ion in water and bases are those compounds or solutions which can take hydrogen ion or hydronium ion in water.
Bronsted-Lowry concept: This was based on the proton acceptor and proton donor. If a compound or solution is a proton donor then it is known as acids and if the solution or compounds are proton acceptor then it is known as bases.
So, if we summarise all these then we can define acids and bases as:
Acids: Those compounds or solutions which can give hydronium ion or proton donor or electron pair acceptors and have pH range $0-7$, are known as acids.
Bases: Those compounds or solutions which are proton acceptor, can accept hydrogen ion or give hydroxide ion, or electron pair donor and have pH range $7-14$, are known as bases.

Note:
Amphoteric Compounds: Those compounds which can act as both acids as well as bases are known as amphoteric compounds. For example: water. Water can release hydrogen ions so can act as acid as well as can give hydroxide ions so can act as base. Hence water is an example of amphoteric.