Which of the following plots are often used for checking randomness in time series?

The correct answer is C. Autocorrelation.

Autocorrelation is a statistical measure of the correlation between a variable and its own lagged values. It is a useful tool for checking randomness in time series data. A time series is said to be random if the autocorrelations of its values decay to zero as the lag increases.

Autocausation is a statistical measure of the correlation between a variable and its own future values. It is not a useful tool for checking randomness in time series data.

Autorank is a statistical measure of the rank correlation between a variable and its own lagged values. It is not a useful tool for checking randomness in time series data.

None of the mentioned is not a valid option.