27) D

__1 – Correct__

Since Cobalt-60 decays by beta, its atomic number increases by 1 and mass number stays the same.

Radiation by gamma does not affect the mass number nor the atomic number.

So after beta decay, the atom’s mass number would be same = 59

Atomic number would be +1 = 27 + 1 = 28.

So Cobalt-60 is converted to ₂₈Nickel.

__2 – Correct__

Since Cobalt – 60 decays by gamma, the tumour is attacked by gamma.

__3 – Wrong__

The radiation attacks all the cells and not just the malignant cells.

Since statements 1 and 2 are correct, D is the answer.