Stationary waves can be produced in

The following statements are given for a stationary wave:
$(a)$ Every particle has a fixed amplitude which is different from the amplitude of its nearest particle.
$(b)$ All the particles cross their mean position at the same time.
$(c)$ All the particles are oscillating with the same amplitude.
$(d)$ There is no net transfer of energy across any plane.
$(e)$ There are some particles which are always at rest.
Which of the following is correct?

Two sinusoidal waves with same wavelengths and amplitudes travel in opposite directions along a string with a speed $10 \, ms^{-1}$. If the minimum time interval between two instants when the string is flat is $0.5 \, s$,the wavelength of the waves is .... $m$

The phase difference between the two particles situated on both the sides of a node in a stationary wave is ... $^o$.

The equation $\overrightarrow{\phi}(x, t) = \overrightarrow{j} \sin \left( \frac{2\pi}{\lambda} vt \right) \cos \left( \frac{2\pi}{\lambda} x \right)$ represents:

Two waves of same frequency $(n)$ approaching each other with same velocity of $18\text{ m/s}$ interfere. The distance between two consecutive antinodes is