is random sample from Rayleigh distribution

1. Show that and than construct unbiased estimator of parameter based on

2. Estimate parameter from following observations:

---Code:16.88 10.23 4.59 6.66 13.68 14.23 19.87 9.40 6.51 10.95

1.I have just plugged in 2 theta in Rayleigh's variance formula and it evaluates to true, but I'm not sure about correct way of constructing unbiased estimator

2.I need help with this one