Question

An electrical circuit for a set of $4$ lights depends on a system of switches $A,B,C$ and $D$. When these switches work they have the following effect on the lights: They each change the state of two lights (i.e. on becomes off and off becomes on). The lights that each switch controls are as follows.

$A$	$B$	$C$	$D$
$1$ and $2$	$2$ and $4$	$1$ and $3$	$3$ and $4$

In configuration $1$ shown below, switches $CBDA$ are activated in turn, resulting in configuration $2$. One switch did not work and had no effect at all. Which was that switch?

• A. $A$
• B. $B$
• C. $C$
• D. $D$

Answer 1

The correct option is C $C$

If all the switches were on the configuration 22 would be:
But the configuration 22 is given as:
There is difference only in Switches 11 and 33. So switch CC is not working