Rarefaction occurs only in a wave.
a. sympathetic.
b. longitudinal.
c. transverse.
d. forced.

The correct answer to the question is : B) Longitudinal wave.

EXPLANATION:

Before coming into any conclusion, first we have to understand the nature of sound wave.

The sound wave is a longitudinal wave in which the direction of vibration of particles are parallel to the direction of wave propagation.

In this type of wave, one will find compression and rarefaction. Compression is the high pressure region in which the particles are closely aggregated to each other.

Rarefaction is the low pressure region in which the particles are far away from each other. There is large separation between particles as compared to compression.

Hence, the correct answer is sound wave.

1. when their charges are of the same signs

Explanation:

Electrostatic force is the force exerted betwen objects that have charge. The magnitude of the force is given by:

where k is the Coulomb constant, q1 and q2 are the charges of the two objects, and r is the separation between the two objects. The sign (and therefore the direction) of the force depends on the relative signs of the two charges. In fact:

- When the two charges have same sign, the force is positive, which means that it is a repulsive force

- When the two charges have opposite sign, the force is negative, which means that it is an attractive force

So, we can conclude that

Two charged objects repel each other when their charges are of the same signs

2. Two terminals, one positive and negative

Explanation:

Batteries are devices which provides (usually through some chemical reactions) a potential difference, also called electromotive force. When connected to a closed circuit, this potential difference provided by the battery "pushes" electrons through the circuit, generating an electric current.

Batteries have generally two terminals: one terminal at positive voltage, called positive terminal, and one terminal at negative voltage, called negative terminal. When connected to the circuit, electrons are pushed from the negative terminal through the circuit towards the positive terminal of the battery.