The problem is to convert the binary number $10101_2$ to its equivalent decimal (base 10) representation.

1. Problem Description

The problem is to convert the binary number $10101_2$ to its equivalent decimal (base 10) representation.

2. Solution Steps

To convert a binary number to a decimal number, we multiply each digit of the binary number by the corresponding power of 2, starting from the rightmost digit with $2^0$, and then sum the results.

$10101_2 = (1 \times 2^4) + (0 \times 2^3) + (1 \times 2^2) + (0 \times 2^1) + (1 \times 2^0)$

$10101_2 = (1 \times 16) + (0 \times 8) + (1 \times 4) + (0 \times 2) + (1 \times 1)$

$10101_2 = 16 + 0 + 4 + 0 + 1$

$10101_2 = 21$

3. Final Answer

The decimal representation of the binary number $10101_2$ is

2

1.