To find the serial number of the word "CORONA" when all the letters are arranged in alphabetical order, we can follow these steps:
### Step 1: Identify the letters and their frequency
The letters in "CORONA" are C, O, R, O, N, A. The frequency of each letter is:
- C: 1
- O: 2
- R: 1
- N: 1
- A: 1
### Step 2: Arrange the letters in alphabetical order
The alphabetical order of the letters is: A, C, N, O, O, R.
### Step 3: Count the arrangements before "CORONA"
We need to count how many arrangements come before "CORONA" in alphabetical order.
#### 3.1: Count arrangements starting with 'A'
If 'A' is the first letter, the remaining letters are C, O, O, R, N. The number of arrangements is calculated as follows:
\[
\text{Arrangements} = \frac{5!}{2!} = \frac{120}{2} = 60
\]
(We divide by \(2!\) because 'O' is repeated.)
#### 3.2: Count arrangements starting with 'C'
Next, we consider arrangements starting with 'C'. The remaining letters are A, O, O, R, N.
##### 3.2.1: Count arrangements starting with 'CA'
If 'CA' is the first part, the remaining letters are O, O, R, N. The number of arrangements is:
\[
\text{Arrangements} = \frac{4!}{2!} = \frac{24}{2} = 12
\]
##### 3.2.2: Count arrangements starting with 'CO'
If 'CO' is the first part, the remaining letters are A, O, R, N. The number of arrangements is:
\[
\text{Arrangements} = 4! = 24
\]
##### 3.2.3: Count arrangements starting with 'C'
Now we consider arrangements starting with 'C', followed by 'N':
- 'C', 'N' followed by A, O, O, R.
###### 3.2.3.1: Count arrangements starting with 'CNO'
If 'CNO' is the first part, the remaining letters are A, O, R. The number of arrangements is:
\[
\text{Arrangements} = 3! = 6
\]
###### 3.2.3.2: Count arrangements starting with 'C'
Now we consider arrangements starting with 'COR':
- 'COR' followed by A, O, N.
###### 3.2.3.2.1: Count arrangements starting with 'CORO'
If 'CORO' is the first part, the remaining letters are A, N. The number of arrangements is:
\[
\text{Arrangements} = 2! = 2
\]
### Step 4: Calculate the total arrangements before "CORONA"
Now we sum all the arrangements:
- Arrangements starting with 'A': 60
- Arrangements starting with 'CA': 12
- Arrangements starting with 'CO': 24
- Arrangements starting with 'CNO': 6
- Arrangements starting with 'CORO': 2
Total arrangements before "CORONA":
\[
60 + 12 + 24 + 6 + 2 = 104
\]
### Step 5: Find the rank of "CORONA"
The rank of "CORONA" is the total arrangements before it plus 1 (for itself):
\[
\text{Rank of CORONA} = 104 + 1 = 105
\]
### Final Answer
The word "CORONA" appears at serial number **105**.
---