The most convenient method to protect the bottom of a ship made of iron is connecting it with Mg block.

Explanation:

Protecting the bottom of a ship made of iron is crucial to prevent corrosion and extend the lifespan of the vessel. The most convenient method to achieve this is by connecting it with a magnesium (Mg) block. Let's understand the reasons behind this choice:

1. Galvanic Protection:
- When two dissimilar metals are in contact with each other in the presence of an electrolyte (such as seawater), galvanic corrosion occurs.
- Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially while protecting the other. The metal that corrodes is called the anode, and the one that is protected is called the cathode.
- In this scenario, the iron hull of the ship acts as the anode, and the magnesium block acts as the cathode.

2. Magnesium as a Sacrificial Anode:
- Magnesium is highly reactive and has a lower electrode potential than iron. Therefore, it will corrode sacrificially to protect the iron hull.
- When connected to the iron hull, the magnesium block will serve as a sacrificial anode, corroding itself instead of the iron.
- This process is known as cathodic protection, where a more active metal (magnesium) is used to protect a less active metal (iron) from corrosion.

3. Advantages of Magnesium:
- Magnesium is an excellent choice for sacrificial anodes due to its high electrochemical potential and ability to provide long-lasting protection.
- It has a higher corrosion rate than iron, ensuring that it corrodes sacrificially while slowing down the corrosion of the iron hull.
- Magnesium anodes are lightweight, making them easier to install and maintain on the ship's bottom.
- They are also cost-effective and readily available, making them a convenient choice for protecting the ship's hull.

In conclusion, connecting the bottom of a ship made of iron with a magnesium block provides galvanic protection by sacrificially corroding the magnesium instead of the iron hull. This method ensures effective and long-lasting corrosion protection, extending the lifespan of the ship.