The correct answer is: B. 25Mhz
The 486DX2 processor is a second-generation x86 microprocessor from Intel. It was introduced in 1992 and was the first processor to use Intel’s patented clock doubling technology, which allowed it to run at twice the speed of its internal clock speed. This meant that a 486DX2 processor running at 50 MHz would have an external clock speed of 25 MHz.
The external clock speed is the speed at which the processor communicates with other components in the system. This includes the memory, the bus, and the peripherals. The external clock speed is typically lower than the internal clock speed because it allows the processor to have more time to process each instruction.
The other options are incorrect because they do not represent the actual external clock speed of a 486DX2 processor.