Hi Vaishnavi!

Q13. The right answer must be option (d) G2/M phase. For detailed explanation of the answer, please refer to the following link: https://youtu.be/OuTQV0m4M8o?feature=shared&t=224  

Q15. The right answer must be option (c) only G2. 

As you must be aware, the DNA content doubles during the S-phase of the cell cycle, where the DNA replicates (here, the chromosome number remains the same but DNA doubles and is visible as another sister chromatid). This doubled DNA content remain same throughout the G2 phase and reduces back to initial amount during Anaphase of M-phase where the sister chromatids separate. Thus, it is evident that the DNA content does not remain doubled during all the stages of M-phase. Hence, it would be appropriate to say, that double DNA content remains only throughout the G2-phase. 

Hope this helps

Thanks