Steric effects in SN2 reactions

• Why do bulky substituents decrease the rate of SN2 reactions?

  Steric hindrance
• What structural property of the substrate affects the rate of SN2 reactions?

  Steric hindrance
• Which type of alkyl halide has the fastest SN2 reaction rate?

  Primary
• What is the phenomenon that results in a lower reaction rate due to fewer available reaction trajectories?

  steric hindrance