I am studying USART, with the help of rs232 and max232 for communication. I want to know if, in a scenario, sender and receiver are following odd parity and except the parity and start, stop bit rest bits gets swapped. So in this case how the receiver will get to know that data received by the receiver is wrong.Here,
Odd/Even parity is not particularly useful for exactly the reason you have identified - it detects only a subset of errors. In days when the number of gates that could fit on chip was far fewer, it had the advantage at least of requiring minimal logic to implement.
However even if you detect an error, what do you do about it? Normally a higher level packet based protocol is used where the packets have a more robust error check such as a CRC. In that case on an error, the receiver can request a resend of the erroneous packet.
At the word rather then packet level, it is possible to use a more sophisticated error checking mechanism by using more bits for error checking and fewer for the data. This reduces the effective data rate further, and on a simple UART requires a software implementation. It is even possible to implement error-detection and correction at the word level, but this is seldom used for UART/USART comms.