Which one of the following statements is not correct?
select one:
a. during allotropic transformation, the number of atoms in the material changes.
b. during allotropic transformation the volume of the material changes.
c. isotopes of the same element have the same number of protons.
d. in an element, the size of its anion is larger than its atomic size

option a, During allotropic transformation, the number of atoms in the material changes.

Explanation:

Allotrops are different crystalline forms of the same element. So, two allotrops of an element have same number of atoms.

for example diamond, graphite, graphene, fullerene are allotropic forms of carbon.

Allpotops differ in physical and chemical properties. So, volume changes during alloptropic transformation. So, statement b is correct.

Allotropic transformation is the transformation of one allotropic form to other therefore, number of atom does not change during allotropic transformation.

Chemical species having same atomic number or same no. of protons are called isotopes. so statement c is correct.

When an electron is added to the neutral element, electronic repulsion increases which lead to the increase in atomic size, So, statement d is also correct.

So among given, option a is incorrect