Arrange the following logic families in the order of increasing speed: CMOS, low power Schottky TTL, ECL, Schottky TTL, low power TTL, TTL : 

The correct answer is option 3.

Comparison between various logic families

CMOS has the lowest operating frequency, hence its time of operation is highest because time is inversely proportional to the operating frequency.

Since the operating time of CMOS is highest, means its speed is lowest.

Similarly, ECL has the highest operating frequency, therefore its time is lowest and hence operating speed is highest.