Extract the answer to the question from the following context. Question: What type of room is least common in the palace? Context: The palace measures 108 metres (354 ft) by 120 metres (390 ft), is 24 metres (79 ft) high and contains over 77,000 m2 (830,000 sq ft) of floorspace. The floor area is smaller than the Royal Palace of Madrid, the Papal Palace in Rome, the Louvre in Paris, the Hofburg Palace in Vienna, or the Forbidden City. There are 775 rooms, including 19 state rooms, 52 principal bedrooms, 188 staff bedrooms, 92 offices, and 78 bathrooms. The principal rooms are contained on the piano nobile behind the west-facing garden façade at the rear of the palace. The centre of this ornate suite of state rooms is the Music Room, its large bow the dominant feature of the façade. Flanking the Music Room are the Blue and the White Drawing Rooms. At the centre of the suite, serving as a corridor to link the state rooms, is the Picture Gallery, which is top-lit and 55 yards (50 m) long. The Gallery is hung with numerous works including some by Rembrandt, van Dyck, Rubens and Vermeer; other rooms leading from the Picture Gallery are the Throne Room and the Green Drawing Room. The Green Drawing Room serves as a huge anteroom to the Throne Room, and is part of the ceremonial route to the throne from the Guard Room at the top of the Grand Staircase. The Guard Room contains white marble statues of Queen Victoria and Prince Albert, in Roman costume, set in a tribune lined with tapestries. These very formal rooms are used only for ceremonial and official entertaining, but are open to the public every summer.
A:
state rooms