(a)
Given vectors are orthogonal.
$\therefore(3x\widehat{\dot{\mathbf{i}}} + y\widehat{\dot{\mathbf{j}}} - 3\widehat{\mathbf{k}}$)∙$\left( x\widehat{\dot{\mathbf{i}}} - 4y\widehat{\dot{\mathbf{j}}} + 4\widehat{\mathbf{k}} \right) = 0$
$\Longrightarrow \ {3x}^{2} - 4y^{2} - 12 = 0$
$\Longrightarrow \ \frac{x^{2}}{4} - \frac{y^{2}}{3} = 1$
Hence, it represent a hyperbola.