Identify components in a circuit diagram and calculate resistance using Ohm's Law, and classify acids and bases based on pH.

The reading of V (ammeter) is the current, $I = 5$ A.  
The reading of IV (voltmeter) is the potential difference, $V = 15$ V.

Ohm's Law states $V = IR$.
$$
R = \frac{V}{I}
$$

$$
R = \frac{15\, \text{V}}{5\, \text{A}} = 3\, \Omega
$$
The value of II is $\boxed{\text{3 } \Omega}$.

Solution A is 0.1 mol dm$^{-3}$ HCl. HCl is a strong acid, so it fully dissociates.

For a strong acid, $[\text{H}^+] = \text{concentration of acid}$.
$$
[\text{H}^+] = 0.1\, \text{mol dm}^{-3} = 10^{-1}\, \text{mol dm}^{-3}
$$
$$
\text{pH} = -\log_{10}[\text{H}^+] = -\log_{10}(10^{-1}) = 1
$$
The pH value of solution A is $\boxed{\text{1}}$.