To calculate the number of characters that can be transmitted per second through an asynchronous serial line, we need to consider the baud rate and the number of stop bits.

Baud rate: The baud rate represents the number of signal changes per second. In this case, the baud rate is given as 2400.

Stop bits: In asynchronous communication, each character transmitted is usually followed by one or two stop bits. The purpose of the stop bits is to allow the receiving device to synchronize with the incoming data. In this case, two stop bits are used.

To calculate the number of characters transmitted per second, we need to consider the time it takes to transmit one character, including start bits, data bits, and stop bits.

- Start bits: In asynchronous communication, each character is usually preceded by one start bit. However, the question does not provide information about the number of start bits, so we will assume there is only one start bit.

- Data bits: The question does not specify the number of data bits in each character. However, since each character code consists of 8 bits, we can assume that each character has 8 data bits.

- Stop bits: The question specifies that two stop bits are used.

Using this information, we can calculate the time it takes to transmit one character:

Time per character = (1 start bit + 8 data bits + 2 stop bits) / baud rate
= (1 + 8 + 2) / 2400
= 11 / 2400 seconds

To calculate the number of characters transmitted per second, we can take the reciprocal of the time per character:

Characters per second = 1 / (11 / 2400)
= 2400 / 11
= 218.18

Since we cannot have a fractional number of characters, we round down to the nearest whole number, which is 218. Therefore, the correct answer is option 'C': 218 characters can be transmitted per second through the asynchronous serial line at a baud rate of 2400 and with two stop bits.

C