Option 1 states that both the assertion (A) and the reason (R) are true, and that R is the correct explanation of A. In this case, A claims that there is a fall in pressure of water along a uniform horizontal pipe, while R states that this is due to the force required to maintain the motion of the liquid against friction.

Option 2 also states that both A and R are true, but R is not the correct explanation of A. This means that while A is true, the reason provided in R is not the correct explanation for why A is true.

Option 3 claims that A is true, but R is false. This means that there is a fall in pressure along the pipe, but it is not due to the force required to maintain the motion of the liquid against friction.

Option 4 states that A is false, but R is true. This means that there is no fall in pressure along the pipe, but force is required to maintain the motion of the liquid against friction.

The correct answer is option 3, as it accurately states that A is true, but R is false. The fall in pressure along the pipe is not due to the force required to maintain the motion of the liquid against friction.