What is the typical relationship between the standard deviation of an individual common stock and the standard deviation of a diversified portfolio of common stocks? The individual stock's standard deviation will be higher

I will explain my point with an example

Let us take a look at these two investments:

Correlation coefficient between returns of ABC & XYZ is 0.6.

The portfolio standard deviation after consideration of correlation:

σ_P = {50%²10%² + 50%² 20%² + 2 × 50% × 50% × 10% × 20% × 0.6 }^1/2
σ_P = 13.6%

Here due to the weight of the individual stock and due to the effect of correlation, the portfolio sd is lower than XYZ and higher than ABC

So it all depends on the individual weights and correlation between the stocks, there is no standard establised relationship between them