The critical field needed to destroy the superconductivity is*1 pointHc = H0 (T/ Tc)Hc = H0 (Tc / T)^2Hc = H0 [ 1 - (Tc / T)^2 ]Hc = H0 [ 1 - (T / Tc )^2 ]

It seems like you've provided multiple options but haven't asked a specific question. These are all formulas for the critical field (Hc) needed to destroy superconductivity, but they are different and would be used under different circumstances or assumptions.

1. Hc = H0 (T/ Tc): This formula suggests that the critical field is directly proportional to the ratio of the absolute temperature (T) to the critical temperature (Tc).

2. Hc = H0 (Tc / T)^2: Here, the critical field is proportional to the square of the ratio of the critical temperature to the absolute temperature.

3. Hc = H0 [ 1 - (Tc / T)^2 ]: In this case, the critical field is given by the initial magnetic field H0 times the quantity [1 - (the square of the ratio of the critical temperature to the absolute temperature)].

4. Hc = H0 [ 1 - (T / Tc )^2 ]: This formula is similar to the previous one, but the ratio of temperatures in the square is flipped.

Without more context or a specific question, it's hard to provide a more detailed answer.