After how much time capacitor is considered as fully charged:

(A) three time constants (3T) 
(B) four time constants (4T) 
(C) five time constants (5T) 
(D) None of these

Answer: (C) five time constants (5T)
After five time constants (5T) it reaches 99.3% charge, so at this point the capacitor is considered to be fully charged.