Two radioactive substances A and B have same number of initial nuclei. If the halflives of A and B are 1.5 days and 4.5 days respectively, then the ratio of the number of nuclei remaining in A and B after 9 days is

• Correct answer
  A

  $1: 16$
• B

  $1: 1$
• C

  $1: 4$
• D

  $1: 8$

Hence, the correct answer is option: 'A'.