Explanation:

1. Relaxed Bacterial Circular Chromosome:
In a relaxed bacterial circular chromosome, the DNA is not under any torsional stress or strain. The DNA molecule is in a relaxed state and is not subjected to any twisting or supercoiling.

2. Helix Turn:
The helix turn is a measure of the number of complete turns made by the DNA helix along the length of the DNA molecule. It is a measure of the helical structure of DNA.

3. Supercoiling:
Supercoiling refers to the twisting or coiling of a DNA molecule upon itself. It can be either positive or negative. In positive supercoiling, the DNA is overwound, while in negative supercoiling, the DNA is underwound.

4. Linking Number:
The linking number (Lk) is a topological property of a closed DNA molecule, such as a circular chromosome. It represents the number of times one strand of DNA crosses over or under the other strand in a closed DNA molecule.

5. Relationship between Linking Number, Helix Turn, and Supercoiling:
The linking number of a circular DNA molecule can be calculated using the formula:

Lk = Tw + Wr

Where Lk is the linking number, Tw is the number of helix turns, and Wr is the number of supercoils.

In the given scenario, the helix turn is 70 and the supercoiling is -10. Since the DNA is supercoiled by -10, Wr is -10.

Thus, the linking number can be calculated as:

Lk = 70 + (-10) = 60

6. The Original Linking Number:
The original linking number refers to the linking number of the DNA molecule in its relaxed state, before any supercoiling or torsional stress is applied. In this case, the DNA is relaxed, so the original linking number is equal to the linking number calculated above, which is 60.

However, it is important to note that the given answer is '70'. This may indicate an error in the question or answer options, as the original linking number should be equal to the calculated linking number (which is 60) in a relaxed state.