Hello, please could someone tell me where the middle coin is in w5-2 also..

World 5-2 Coin 2:
After you get the first coin, continue until you see a yellow pipe on the ceiling. Go through it to go above ground to where you'll find Coin 2.

World 5-C Coin 3:
Right after you get the second coin, there should be an arch of four regular coins over a pit, followed by a row of brick blocks. Jump on top of these, and break as many blocks in the ceiling as you can. Then go back down and hit the last block on the right. A vine will grow, allowing you to climb up the vine. If you didn't clear the blocks away, it won't grow all the way up.

Once you're up there, make your way to the P Switch, but don' hit it. Wait until the Broozer is on the left side of the platform, hit the switch. Run on top of the brown blocks over the Star Coin to make the Broozer smash the blocks away. He'll fall into a pit, and you can grab the Star Coin. Once the P Switch shuts off, you can fall down the hole with the coins to land near the level end.