The correct option is B Metaphase
Mitosis is divided into the following four stages. They are prophase, metaphase, anaphase and telophase.The complete disintegration of the nuclear envelope marks the start of the metaphase (second phase of mitosis).Best stage to observe shape, size and number of chromosomes are metaphase because, by this stage, condensation of chromosomes is completed and they can be observed clearly under the microscope.So, the correct answer is 'Metaphase'.