What is parity bit used for?

a) In above table, nine bytes of data have been transmitted. Another byte, known as the parity byte, has also been sent (this byte consists entirely of the parity bits produced by the vertical parity check and indicates the end of the block of data). Even parity is being used. The table shows how the data arrived at the receiving end. And each row and column need to be checked to see if they still show even parity. Which rows and columns show incorrect parity?

b) In which cases parity bit has a limitation? Give an example (You can use this table, or you can write your own example).

\begin{tabular}{|l|l|l|l|l|l|l|l|l|} \hline & \begin{tabular}{l} Parity \\ bit \end{tabular} & Bit 2 & Bit 3 & Bit 4 & Bit 5 & Bit 6 & Bit 7 & Bit 8 \\ \hline Byte 1 & 1 & 1 & 1 & 1 & 0 & 1 & 1 & 0 \\ \hline Byte 2 & 1 & 0 & 0 & 1 & 0 & 1 & 0 & 1 \\ \hline Byte 3 & 0 & 1 & 1 & 1 & 1 & 1 & 1 & 0 \\ \hline Byte 4 & 1 & 0 & 0 & 0 & 0 & 0 & 1 & 0 \\ \hline Byte 5 & 0 & 1 & 1 & 0 & 1 & 0 & 0 & 1 \\ \hline Byte 6 & 1 & 0 & 0 & 0 & 1 & 0 & 0 & 0 \\ \hline Byte 7 & 1 & 0 & 1 & 0 & 1 & 1 & 1 & 1 \\ \hline Byte 8 & 0 & 0 & 0 & 1 & 1 & 0 & 1 & 0 \\ \hline Byte 9 & 0 & 0 & 0 & 1 & 0 & 0 & 1 & 0 \\ \hline \begin{tabular}{l} Parity \\ byte \end{tabular} & 1 & 1 & 0 & 1 & 0 & 0 & 0 & 1 \\ \hline \end{tabular}