Presenting problem - A 25 year old man presents with a 5-day history of right sided chest pain and describes it as a 'catch in breath'. It gets worse with deep breathing and coughing. During this period, he has developed fever, which is more pronounced in the evening. He also complains of dry cough. Over the past two days, he has developed breathlessness, which has worsened rapidly. He does not complain of rash, oral ulcers, photosensitivity or joint pains. He is an otherwise healthy bank clerk who has not suffered from any other illness. He does not smoke or drink alcohol and is not taking any medication. Physical examination reveals mild Pallor. His pulse is regular at 110beats/min and his BP is 120/82mmHg. Respiratory rate is 26/min. There is no evidence of a rash, oral ulcers, arthritis, or peripheral lymphadenopathy. Signs of liver cell failure are absent. The trachea is shifted to the left side and the apical impulse is shifted laterally. The right side of the chest moves less with respiration. Tactile vocal fremitus is reduced. On percussion, a stony dull note is elicited on the right side and this dullness does not shift with change in posture. Breath sounds and vocal resonance are almost absent on the right side. There is no succusion splash. Abdominal, cardiovascular and neuro examinations are normal. What is the probable diagnosis? What are the investigations to be carried out to confirm the diagnosis?