Assertion : $$\mathrm{S}_2 \mathrm{O}_7^{2-}$$ and $$\mathrm{Cr}_2 \mathrm{O}_7^{2-}$$ both exist.

Reason : Both have same valence electrons.

Assertion : $$\mathrm{Yb}^{2+}$$ is more stable in compare to $$\mathrm{Gd}^{+2}$$.

Reason : The electronic configuration of GD is $$[\mathrm{Xe}] 4 f^7 5 d^2 6 s^2$$.

Assertion : $$d^5$$ configuration is more stable than $$d^4$$.

Reason : $$d^5$$ has more exchange energy as compared to $$d^4$$ because 10 and 6 exchanges are possible in $$d^5$$ and $$d^4$$ respectively.