A spherical naphthalene ball of $2\:mm$ diameter is subliming very slowly in stagnant air at $25^{\circ}C$. The change in the size of the ball during the sublimation can be neglected. The diffusivity of naphthalene in air at $25^{\circ}C$ is $1.1\times10^{-6}\:m^2/s$.

The value of mass transfer coefficient is $B\times10^{-3}\:m/s$, where $B$ (up to one decimal place) is ____________ .