This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Shrinkage due to loss of water and alcohol is seen in: \nSelect and explain. \nA. Silica bonded, B. Gypsum bonded, C. Magnesium bonded, D. Phosphate bonded', 'role': 'user'}, {'content': 'Answer: A \nExplanation: SILICA BONDED INVESTMENTS\xa0\nThe silica is the binder. It is derived from ethyl silicate or aqueous dispersion of colloidal silica or sodium silicate. These are less commonly used.\xa0\nTYPES\xa0\nBased on the binder used two types may be seen. One such investment consists of silica refractory, which is bonded by the hydrolysis of ethyl silicate in the presence of hydrochloric acid. The product of the hydrolysis is the formation of a colloidal solution of silicic acid and ethyl alcohol.', 'role': 'assistant'}]