A material is said to be allotropic, if it has

The correct answer is 3 only

Key Points

• Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Hence, statement 1 is incorrect.
•  it has different crystal structures at different temperatures.
• For example, the allotropes of carbon include:
  • Diamond (the carbon atoms are bonded together in a tetrahedral lattice arrangement)
  • Graphite (the carbon atoms are bonded together in sheets of a hexagonal lattice)
  • Graphene (single sheets of graphite)
  • Fullerenes (the carbon atoms are bonded together in spherical, tubular, or ellipsoidal formations). 
• The term allotropy is used for elements only, not for compounds. Hence, statement 2 is correct.
• The more general term, used for any crystalline material, is polymorphism.
• Allotropy refers only to different forms of an element within the same phase (i.e.: solid, liquid, or gas states); the differences between these states would not alone constitute examples of allotropy