Final answer:
In Marxist theory, when capital is converted into common property, personal property transforms into social property.
Step-by-step explanation:
In Marxist theory, when capital is converted into common property, personal property transforms into social property (option a). According to Marx, in a socialist society, the means of production are collectively owned and controlled by the workers or the state, rather than being owned by individuals. This includes both capital and personal property. The goal of socialism is to eliminate class distinctions and create a more equitable society.