Which of the following is a secondary alkyl halide
Well, no. Here is the quote from Wikipedia:


  From the structural perspective, haloalkanes can be classified
  according to the connectivity of the carbon atom to which the halogen
  is attached. In primary (1°) haloalkanes, the carbon that carries the
  halogen atom is only attached to one other alkyl group. An example is
  chloroethane ($\ce{CH3CH2Cl}$). In secondary (2°) haloalkanes, the carbon
  that carries the halogen atom has two $\ce{C–C}$ bonds. In tertiary (3°)
  haloalkanes, the carbon that carries the halogen atom has three $\ce{C–C}$ 
  bonds.


So, the presence of $\ce{CH2Cl}$, $\ce{CHCl}$, and $\ce{CCl}$ are the indicators of primary, secondary, and tertiary haloalkane respectively.

Here is b with the $\ce{C}$ atom to which $\ce{Cl}$ is attached as well as its two $\ce{C–C}$ bonds highlighted in red.