Refer to figure.
The Figure 2.17 refers to a Single-Engined Piston Helicopter.

For a single engine helicopter, the Height-Velocity (H-V) envelope defines a combination of airspeed and height above the ground from which the helicopter will probably not be able to enter autorotation and a safe landing will not be assured. Therefore, the shaded areas of the H-V graph are not prohibited, but should be avoided, so Statement 1 is incorrect.

Operations at any height or speed within the shaded areas are likely to result in a crash landing. In order to give the best possible margin from both lower and upper shaded areas, the recommended take-off profile is flown by the Pilot, depicted by the dashed line. So, Statement 2 is correct.

As shown in the figure, for any combination of height and speed along the dashed line from 25 ft and on, the recommended take-off speed is constant 61 kt IAS. So, Statement 3 is incorrect.

According to CS-29.87 Height-Velocity Envelope:

(a) If there is any combination of height and forward velocity (including hover) under which a safe landing cannot be made after failure of the critical engine and with the remaining engines (where applicable) operating within approved limits, a height-velocity envelope must be established for:

(1) All combinations of pressure altitude and ambient temperature for which take-off and landing are approved; and

(2) Weight, from the maximum weight (at sea-level) to the highest weight approved for take-off and landing at each altitude. For helicopters, this weight need not exceed the highest weight allowing hovering out of ground effect at each altitude.

(b) For single engine or multi-engine rotorcraft that do not meet the Category A engine isolation requirements, the height-velocity envelope for complete power failure must be established.

According to CS-27.2, the above paragraphs of CS-29 must be met for CS-27, too.

So, Statement 4 is correct.