Refer to figures.
Carburettor icing occurs when moisture in the induction air freezes in the venturi throat of the carburettor due to the temperature drop caused by two combined effects: 

• The pressure drop and Velocity increase at the venturi
• The latent heat absorbed by evaporating fuel droplets

Together these effects can reduce the local temperature inside the carburettor by up to 35°C below the ambient OAT. This means that even with an outside air temperature of +25°C, the temperature inside the carburettor can drop to approximately -10°C, well below the freezing point of water, causing moisture to freeze on the venturi walls. Carburettor icing therefore does NOT require precipitation or sub-zero ambient temperatures. It is most dangerous in warm, humid air (OAT between 0°C and +25°C with high relative humidity) precisely because the warm air contains large quantities of water vapour that can freeze inside the carburettor despite the benign external conditions.

It is particularly hazardous at low power settings (descent, approach) where the venturi effect is greatest relative to the throttle opening.

At temperatures up to +25°C in humid air → CORRECT. Carburettor icing is most dangerous in warm humid conditions. The venturi cooling effect can reduce the internal temperature by up to 35°C, meaning an OAT of +25°C can produce carburettor throat temperatures around -10°C. High humidity provides the water vapour that freezes to form the ice. This is the correct and well-established carburettor icing risk condition.

Only when the outside air temperature is below 0°C → INCORRECT. Carburettor icing is most insidious precisely because it occurs when OAT is well ABOVE freezing (0 to +25°C). If pilots only watched for sub-zero temperatures they would miss the most hazardous icing conditions, which occur in warm humid air.

During high power settings in very dry air → INCORRECT. High power settings actually REDUCE carburettor icing risk because the increased fuel flow raises carburettor temperatures. Carburettor icing is most likely at LOW power settings (reduced fuel flow, greater relative venturi cooling effect). Dry air also reduces risk because there is less moisture available to freeze.

Only when flying through visible liquid precipitation → INCORRECT. Carburettor icing occurs in clear air with no precipitation. The moisture source is water vapour in the air, not liquid precipitation. Flying through rain does not significantly increase carburettor icing risk compared to high-humidity clear air. The clear-air humid conditions are the primary risk scenario.