What is nucleophilic catalysis?

What is the trend in atomic size for group 7A halogens as you move down the group?

What happens to the stereochemistry of a molecule undergoing an SN2 reaction?

Why is iodine considered a better leaving group than chlorine in nucleophilic catalysis?

If an uncatalyzed reaction has a rate of 0.1 M/s and the catalyzed reaction has a rate of 1.0 M/s, what is the rate increase?