Must one make up for missed fasting and prayers if blood appears several days after the cessation of menstruation and ritual purification, and one does not know whether it is menstrual blood or not?

If the blood reappears on the tenth or fifteenth day and does not exceed the fifteenth, it is menstrual blood, and you must perform ghusl after its cessation. As for the days of purity that preceded the return of the blood, your purity during them is valid, and you are not required to make up for the acts of worship you performed. The day you saw the blood invalidates your fast, and you are required to make it up if it was obligatory, just as you are required to repeat the prayers you performed after seeing the blood if you had not performed ghusl. If you doubt the time of the blood's discharge, it is to be attributed to the closest probable time of its occurrence, and if you doubt between the tenth and fifteenth day, estimate it as the fifteenth.