Physics
In a bipolar junction transistor

The emitter has the least concentration of impurity
All the three regions (the emitter, the base and the collector) have equal concentrations of impurity
The collector has the least concentration of impurity
The base has the least concentration of impurity

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Physics
On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because:

cohesion of water is greater than its adhesion with glass.
cohesion of mercury is greater than its adhesion with glass.
mercury is a metal.
density of mercury is greater than that of water.

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