Knob and Tube is wiring that is secured by porcelain knobs and tubes. The problem with knob and tube is the wires in basements and attics are very exposed and susceptible to damage. This wiring system is also around 100 or more years old. Damaged wires can be both a shocking and fire hazard.
Aluminum wiring was only used for around 10- 15 years in the 60’s and 70’s. Aluminum can be a safe conductor if used and maintained correctly, but it can oxidize or corrode much faster than copper. Aluminum also oxidizes when paired with many other metals. This is why a mix of copper and aluminum is particularly dangerous. When an aluminum conductor corrodes it creates arcing and that is how many house fires begin.