To understand the relationship between the mass of a substance deposited at an electrode and the quantity of electricity passed through an electrolyte, we refer to Faraday's laws of electrolysis. These laws are vital in the field of electrochemistry:

1. Faraday's First Law of Electrolysis: This law states that the mass of a substance (m) deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity (Q) passed through the electrolyte. Mathematically, it is represented as: m \propto Q, or m = ZQ where Z is the electrochemical equivalent.
2. Faraday's Second Law of Electrolysis: This law says that when the same quantity of electricity is passed through different electrolytes, the mass of substances deposited are directly proportional to their chemical equivalents.

Given that the mass of a substance deposited (m) is directly proportional to the quantity of electricity (Q) passed, if the quantity of electricity is increased, then the mass deposited at the electrode will also increase, assuming other factors remain constant.

Therefore, based on Faraday's laws, the correct conclusion is that:

The mass deposited increases.

Let's briefly analyze the given options:

• The mass deposited increases: This is the correct answer according to Faraday's First Law.
• The mass deposited changes unpredictably: This is incorrect because the relationship between electricity and mass is predictable.
• The mass deposited remains constant: This is incorrect because increasing the electricity will increase the mass deposited.
• The mass deposited decreases: This is incorrect since increasing electricity does not decrease the deposited mass.