Select the total number of correct statements about loop of Henle:

1. Descending limb is permeable to water.

2. Descending limb is almost impermeable to electrolyte.

3. Ascending limb is impermeable to water.

4. It allows the transport of electrolyte only actively.

5. At the tip of loop of Henle, the concentration of filtrate is 1200 m osmol/L.

6. It helps in the maintenance of high osmolarity in the medullary interstitium.