The correct answer is A. lowered.
A hydrometer is a device used to measure the specific gravity of liquids. It is a glass tube with a weighted bulb at one end and a graduated scale at the other. The hydrometer is placed in the liquid and the level at which it floats is read on the scale. The specific gravity of the liquid is then determined by comparing the reading on the scale to the reading for water.
In order for a hydrometer to float vertically in electrolyte, its center of gravity (CG) must be below the surface of the liquid. This is because the buoyant force of the liquid acts upwards on the hydrometer, and the weight of the hydrometer acts downwards. If the CG is above the surface of the liquid, the hydrometer will tip over.
If the CG is lowered, the hydrometer will be more stable and will float more vertically. This is because the buoyant force will act more directly downwards, and the weight of the hydrometer will act more directly upwards.
The other options are incorrect because they would not cause the hydrometer to float vertically. Option B, raised, would cause the hydrometer to tip over. Option C, undisturbed, would not change the position of the hydrometer. Option D, displaced sideways, would cause the hydrometer to float at an angle.