Question

the wells that contain the dna samples are placed next to the negatively charged electrode in the electrophoresis box (chamber) because

dna is positively charged

dna is negatively charged

dna has no electrical charge

dna strands have both a positive and a negative charge

Explanation:

DNA has a negative charge due to the phosphate groups in its backbone. In electrophoresis, opposite charges attract. So, placing DNA (negatively charged) near the negative electrode would be incorrect as like charges repel. Wait, no - in electrophoresis, the DNA migrates towards the positive electrode. But the question is about why the wells (containing DNA) are placed next to the negative electrode. Because DNA is negatively charged. Opposite charges attract. But in the setup, the electric field is such that when voltage is applied, the negatively - charged DNA will move towards the positive electrode. So, to start the movement (since opposite charges attract conceptually in the setup), the DNA (negatively charged) is placed near the negative electrode (so that when the field is on, it moves towards positive).

Answer:

DNA is negatively charged