If investors want portfolios with small risk (variance), should they look for investments that have positive covariance, have negative covariance, or are uncorrelated? What is the covariance between...

If investors want portfolios with small risk (variance), should they look for investments that have positive covariance, have negative covariance, or are uncorrelated?

What is the covariance between the random variable
 and itself, Cov ()? What is the correlation between a random variable and itself?