Final answer:
Characteristic properties of elements include both physical properties like color, density, and melting points, and chemical properties like flammability and reactivity with acid. Options (a) and (d) partially describe these characteristic properties, with option (a) listing physical properties and option (d) listing chemical properties.
Step-by-step explanation:
The characteristic properties of elements can be divided into physical properties and chemical properties. Physical properties include characteristics such as color, density, and melting and boiling points, which can be observed or measured without changing the identity of the substance. Chemical properties describe the ability of a substance to undergo a specific chemical change, such as flammability and reactivity with acid, which involve altering the substance's chemical structure or composition.
With reference to the options provided in the question, option (a) size, melting point, and density are physical properties, while option (d) flammability and reactivity with acid are chemical properties. Weight, however, is a measure of gravitational force and not a characteristic property used to classify materials. Thus, while options (a) and (d) contain elements of the correct answer, neither is entirely accurate as they are presented.