R3 has dimension 3. So, a set of 3 vectors in R3 will span R3 as long as the set is linearly independent.
The vectors are linearly independent if the only real numbers a, b, c such that
a(2,0,1) + b(1,1,0) + c(0,0,1) = (0,0,0) are a = b = c = 0.
From the equation above, we have 2a + b = 0, b = 0 and a + c = 0.
It's easy to see that a, b, and c must all be zero.
So, the set is linearly independent and must span R3.