What is bond angle $\mathrm{F}-\mathrm{B}-\mathrm{F}$ in $\mathrm{BF}_3$ ?

Which from the following statements about $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$ complex is NOT correct?

What is the relation between edge length and total volume occupied by atoms in bec unit cell?

What is the value of $x$ and $y$ in order to balance following redox reaction?

$$\mathrm{xCuO}+\mathrm{yNH}_3 \longrightarrow \mathrm{xCu}+\mathrm{N}_2+\mathrm{xH}_2 \mathrm{O}$$