What is the main difference between a circular loop and a solenoid?

The adjacent diagram shows a small magnet placed near a solenoid $AB$ with its north pole $N$ near the end $A$. Current is switched on in the solenoid by pressing the key $K.$ State the polarity at the ends $A$ and $B.$ Give a reason for your answer.

The figure below shows two loops of radii $r$ and $\raisebox{1ex}{$r$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ and having number of turns $n$ and $2n$ respectively. Calculate the ratio of magnetic field induced in the two loops when same current is passed in these loops. 

The adjacent diagram shows a small magnet placed near a solenoid $AB$ with its north pole $N$ near the end $A$. Current is switched on in the solenoid by pressing the key $K.$ Will the magnet be attracted or repelled ? Give a reason for your answer.