JEE Math Practice Question

Consider the relations $R_1$ and $R_2$ defined as $a R_1 b \Leftrightarrow a^2+b^2=1$ for all $a, b \in \mathbf{R}$ and $(a, b) R_2(c, d) \Leftrightarrow$ $a+d=b+c$ for all $(a, b),(c, d) \in \mathbf{N} \times \mathbf{N}$. Then :

1. A.$R_1$ and $R_2$ both are equivalence relations
2. B.Only $R_1$ is an equivalence relation
3. C.Only $R_2$ is an equivalence relation
4. D.Neither $R_1$ nor $R_2$ is an equivalence relation