In a one-step binomial model, the price of a call option can be calculated using the following formula:

[ \text{Call Price} = (Up Move Outcome Probability) * (Payoff if Up) + (Down Move Outcome) * (Payoff if Down) ]

Given the up move probability ( p^ ), the down move probability (1 - p^), the up factor u, the down factor d, and the strike price SO (Strike Option) or the exercise price of the option, the call option price can be calculated as follows:

[ \text{Call Price} = p^ \times (u \cdot (SO - SO)) + (1 - p^) \times (SO - d \cdot SO) ]

Given the values provided in the question (r = 0, u = 1.1, d = 0.8, and SO = 100), we can calculate the call option price:

[ \text{Call Price} = p^ \times (1.1 \cdot 100 - 100) + (1 - p^) \times (100 - 0.8 \cdot 100)]

However, since we don't have the risk-neutral up probability ( p^* ), we cannot calculate the exact price without it. Therefore, the correct answer is:

c. We cannot calculate it as the strike K is not given

So, the correct answer is:

c. We cannot calculate it as the strike K is not given