According to Fajan's rules, which of the following is not correct about covalent character?
Consider the following (unbalanced) reactions:
\[ \text{BF}_3 + \text{NaH} \xrightarrow{450\,\mathrm{K}} X + \text{NaF} \]
\[ X + \text{H}_2\text{O} \rightarrow Y + \text{H}_2 \uparrow \]
The correct statements about \(X\) and \(Y\) are:
If \( \sqrt{5} - i\sqrt{15} = r(\cos\theta + i\sin\theta), -\pi < \theta < \pi, \) then
\[ r^2(\sec\theta + 3\csc^2\theta) = \]
The system of simultaneous linear equations :
\[ \begin{array}{rcl} x - 2y + 3z &=& 4 \\ 2x + 3y + z &=& 6 \\ 3x + y - 2z &=& 7 \end{array} \]
Calculate the determinant of the matrix: