Which of the following is/are EQUAL to 224 in radix-5 ($i.e.$, base-5) notation?

To find which options are equivalent, convert $(224)_5$ into decimal (radix-10):

Now, convert each option to decimal:

• Option A: $64$ in radix-10 is $64_{10}$. *(Matches)*

• Option B: $(100)_8 = 1 \times 8^2 + 0 \times 8^1 + 0 \times 8^0 = 64_{10}$. *(Matches)*

• Option C: $(50)_{16} = 5 \times 16^1 + 0 \times 16^0 = 80_{10} \neq 64_{10}$. *(Does not match)*

• Option D: $(121)_7 = 1 \times 7^2 + 2 \times 7^1 + 1 \times 7^0 = 49 + 14 + 1 = 64_{10}$. *(Matches)*

Therefore, options A, B, and D are correct.