The binary number 10101 is equivalent to decimal number ___________.

A).  19

B).  12

C).  27

D).  21

 21

Solution:

Given: Binary number = 10101 

Decimal number = ?

To convert a binary number into decimal number we have to multiply each term of the binary number individually by 2^n where n is the place value of each term.

$(10101)_2 = (1 × 2⁰) + (0 × 2¹) + (1 × 2²) + (0 × 2³) + (1 × 2⁴)$

$= 1 + 4 + 16$

$= (21)_{10}$

So, the decimal number is 21.

The correct option is D).21

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