Why does specific conductivity increase with depth in lakes?

Conductivity is a measure of capability of water to pass the electrical flow. It has direct links with the presence and concentration of ions which come from dissolved salts and inorganic material like chloride, sulfides present in water.

Conductivity increases with the increase in the depth of the lake because of the presence and concentration of these ions in the depth and in lesser amount at the surface resulting in higher conductivity.

d is the logical answer but im not a 100% sure

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