What is the primary effect of a condenser connected across contact points in a DC circuit?

The correct answer is that a condenser connected across contact points in a DC circuit primarily serves to store energy. When a capacitor (or condenser) is connected across the contacts, it accumulates electrical charge and thus stores energy in the form of an electric field. This capability to store energy can help in smoothing out voltage spikes, filtering noise, or providing temporary power during brief interruptions in supply.

While capacitors can influence other aspects of a circuit, such as transient response or stability, their fundamental role aligns with energy storage. In the context of this question, this storage effect can be crucial for maintaining voltage levels and ensuring that the circuit operates smoothly, particularly in DC circuits where maintaining stability is important.

The other options, like increasing inductance or controlling thermal dissipation, are not directly related to the functionality of a capacitor in this scenario. A capacitor does not inherently increase inductance, as that pertains to inductors, and while capacitors can influence dissipation under certain conditions, their primary function is tied to their ability to store and release electrical energy as needed. Thus, option B correctly captures the essence of a capacitor's role in this context.