A phenomenon by which an element occurs in different physical modification in same physical state is calledA isomerism B allotropy C amorphous D crystalline

The phenomenon by which an element occurs in different physical modifications in the same physical state is called allotropy. So, the correct answer is B. Allotropy.

Here's a step-by-step explanation:

1. Isomerism is a phenomenon in which compounds have the same molecular formula but different structural formulas. This is not the correct answer because the question is asking about different physical modifications of the same element, not different structures of the same compound.

2. Allotropy 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. Allotropes are different structural modifications of an element; the atoms of the element are bonded together in a different manner. This fits the description given in the question.

3. Amorphous and crystalline are terms used to describe the arrangement of atoms in a solid. Amorphous solids have a random, disordered arrangement of atoms, while crystalline solids have a highly ordered, repeating arrangement of atoms. These terms describe types of solids, not phenomena related to the physical modifications of elements.

So, the correct answer is B. Allotropy.