For a unidirectional first order decomposition:

$X\text{(}g\text{)}\stackrel{ }{\to }Y\left(g\right)+2Z\left(g\right)$

Pure $X\left(g\right)$ is taken in an evacuated flask at t = 0. After 10 seconds, a pin-hole is made in the flask and the gaseous mixture is allowed to effuse out into a vacuum. Analysis of the initial effused mixture reveals that moles of Z(g) were double the moles of X(g). If molar masses of X, Y and Z are 16, 8 and 4 respectively, rate constant for the decomposition of X is _________  ${\sec }^{-1}.$