How would I approach this proof?

4. Consider a set of vectors {v1, V2, ..., VK} in R". Two vectors v1, 12 E R" are said to be orthogonal if 1 12 = 0. Suppose the set of vectors {v1, v2, . .., VK} are mutually (pair-wise) orthogonal. 1. Show that {v1, V2, ..., VK} must be LI. 2. Conclude that k must be less than or equal to n. Why? 3. For what value of k are these vectors a basis of Rn