The colour sequence in a carbon resistor is red, brown, orange, and silver. Then find the resistance of the resistor.
A. \[21 \times {10^3} \pm 10\% \]
B. \[23 \times {10^1} \pm 10\% \]
C. \[21 \times {10^3} \pm 5\% \]
D. \[12 \times {10^3} \pm 5\% \]

Hint: Here, the resistance and tolerance of a resistor is marked on the resistor by using the colour bands. This colour band used is generally called the resistance colour code. In order to solve this question, we use the colour code chart of resistance.

Complete step by step solution:
Here, we have a resistor with four colour bands on it, which are red, brown, orange, and silver. Here, we are going to find the resistance of the resistor. In order to find this, we have a resistor colour code chart.


Here the first colour given is ‘red’. The first colour band on the resistor is the first significant digit of resistance. According to the given chart, the significant digit for red is 2.
Second colour band is the second significant figure of resistance.
Second colour here is brown.
We know the significant digit for brown is 1.
Then the third colour band is the decimal multiplier of the first two significant digits.
Third band here is orange.
From the colour code chart, the multiplier value of orange is \[{10^3}\].
The fourth band will give the tolerance of the resistance.
Fourth band given here is silver.
Tolerance of gold \[ \pm 10\]
Therefore, the resistance value of the resistor with colour code red, brown, orange, and silver is \[21 \times {10^3} \pm 10\% \].

Hence, option A is the correct answer.

Note:Here, in this problem it is important to remember the colour code chart from which we can find the value of any given resistor. We also have the code called BBROY of Great Britain Has a Very Good Wife Wearing Gold Silver Necklace. Every uppercase here represents the colours in sequence.