Final answer:
To complete a mechanistic step, you need to draw electron pushing arrows to show the flow of electrons during a reaction.
Step-by-step explanation:
The question asks you to complete a mechanistic step by drawing in the electron pushing arrows. To do this, you need to consider the movement of electrons during a reaction. The arrows represent the flow of electrons from one atom to another.
For example, in a reaction between potassium (K) and sulfur (S) to form potassium sulfide (K2S), the electron pushing arrows would show the transfer of electrons from K to S. The arrows would point from K to S to indicate the flow of electrons.
In the case of H-Cl, the arrow would point from H to Cl because chlorine is more electronegative than hydrogen.