The threshold frequency for potassium (in joule) is $3\cdot 0\times {10}^{14}$per sec. The work function of potassium is

• A

  $0\cdot 5\times {10}^{-19}$

• B

  $1\cdot 0\times {10}^{-19}$

• C

  $2\cdot 0\times {10}^{-19}$

• D

  $4\cdot 0\times {10}^{-19}$