Determine the best description for activation energy (Question 1.1).

Activation energy is the minimum energy required for reactant particles to collide with sufficient energy to break existing bonds and form new ones, leading to a chemical reaction. This is known as an effective collision.

The correct option is B.

Curve I represents the reaction of powdered magnesium with 1 mol·dm⁻³ HCl at 25 °C.
Curve II shows a faster reaction rate (steeper slope) but produces the same final volume of hydrogen gas as Curve I. The problem states the same volume of hydrochloric acid solution was used for both curves.

For the final volume of hydrogen gas to be the same, the initial amount (moles) of the limiting reactant (HCl, as Mg is in excess) must be the same. Since the volume of HCl solution is the same, its concentration must also be the same for both curves. This means the concentration for Curve II must be 1 mol·dm⁻³.

For the reaction rate to be faster, either the surface area of magnesium, the concentration of HCl, or the temperature must be increased. Since the concentration is the same, we look for an increase in surface area or temperature.

Let's evaluate the options:

• A: Ribbon Mg (smaller surface area, slower rate) and 0.5 mol·dm⁻³ acid (lower concentration, less product). Incorrect.
• B: Ribbon Mg (smaller surface area, slower rate) but 2 mol·dm⁻³ acid (higher concentration, more product). Incorrect.
• C: Powdered Mg (same surface area) and 1 mol·dm⁻³ acid (same concentration) but 20 °C (lower temperature, slower rate). Incorrect.
• D: Powdered Mg (same surface area) and 1 mol·dm⁻³ acid (same concentration) but 30 °C (higher temperature, faster rate). This option matches both criteria: same concentration (1 mol·dm⁻³) for the same product volume, and higher temperature (30 °C > 25 °C) for a faster reaction rate.

The correct option is D.

Final Answer:

1.1: $\boxed{\text{B}}$

1.2: $\boxed{\text{D}}$