Identify the numerical variables with zero variance $($i$.$e$.,$ zero standard deviation$)$ and save them in a LIST

Drop these numerical variables with zero variance $($i$.$e$.,$ zero standard deviation$)$ from the dataset df$.$ The dataset df should not have these variables going forward.

Hints:

For each numerical variable, compute the standard deviation. If the standard deviation is zero, delete $($i$.$e$.,$ drop$)$ that variable from the dataset df$.$Check Modules $5$b: Dropping Variables