Which statement from the following about nanomaterials is $NOT$ correct?

• A
  As the particle size decreases,the total surface area of particles increases.
• B
  Nanomaterial-based catalysts exhibit increased catalytic activities.
• C
  Nanosized $Cu$ and $Pd$ clusters have very less hardness than bulk metal.
• D
  Carbon nanotubes can act as electrical conductors.