To convert a binary number to a decimal number, we need to follow these steps:

Write down the binary number and assign a power of 2 to each digit, starting from the rightmost with 2^0.

Convert each binary digit to its decimal equivalent by multiplying it with its power of 2.

Add all the decimal values to get the decimal equivalent of the binary number.

Let’s apply these steps to the binary number 10001010:

10001010 = 0 × 2^0 + 1 × 2^1 + 0 × 2^2 + 1 × 2^3 + 0 × 2^4 + 0 × 2^5 + 0 × 2^6 + 1 × 2^7

10001010 = 0 + 2 + 0 + 8 + 0 + 0 + 0 + 128

10001010 = 138 in decimal

Therefore, the decimal equivalent of the binary number 10001010 is 138 (option A).

References: The answer can be verified by using the following resources:

Convert 10001010 from binary to decimal - Calculator Online

How to Convert decimal number 10001010 in binary? - CoolConversion

10001010 to decimal - Calculatio

Binary Code | Binary: 10001010 | Decimal: 138 | Bits: 8