Concept:
For a particle executing Simple Harmonic Motion (SHM) starting from the positive extreme position, its displacement \(x\) at any time \(t\) is given by the cosine function:
\[
x = A \cos(\omega t)
\]
where \(A\) is the amplitude and \(\omega\) is the angular frequency.
Step 1: Identifying given parameters and calculating angular frequency.
Given:
• Amplitude, \(A = 4\text{ cm}\)
• Time period, \(T = 4\text{ s}\)
Angular frequency \(\omega\) is:
\[
\omega = \frac{2\pi}{T} = \frac{2\pi}{4} = \frac{\pi}{2} \text{ rad/s}
\]
The target position is half the amplitude:
\[
x = \frac{A}{2} = \frac{4}{2} = 2\text{ cm}
\]
Step 2: Applying the displacement equation.
Since the particle starts from the positive extreme, we use:
\[
x = A \cos(\omega t)
\]
Substitute the values of \(x\), \(A\), and \(\omega\):
\[
2 = 4 \cos\left(\frac{\pi}{2} t\right)
\]
\[
\cos\left(\frac{\pi}{2} t\right) = \frac{2}{4} = \frac{1}{2}
\]
Step 3: Solving for time \(t\).
We know that \(\cos\left(\frac{\pi}{3}\right) = \frac{1}{2}\). Therefore:
\[
\frac{\pi}{2} t = \frac{\pi}{3}
\]
Solving for \(t\):
\[
t = \frac{\pi}{3} \times \frac{2}{\pi}
\]
\[
t = \frac{2}{3} \text{ s}
\]
Step 4: Selecting the correct option.
From the calculation above, the time taken is:
\[
\boxed{\frac{2}{3}\text{ s}}
\]
Therefore, the correct option is:
\[
\boxed{\text{Option (C)}}
\]