The de Broglie wavelength is inversely proportional to the momentum of the particle.

The velocity (momentum) is proportional to the square root of the potential V.

The de Broglie wavelength is inversely proportional to the square root of the potential difference, V.

 

Hint ....write the things down on paper and work it out. Try not to guess or to work it out in your head. No extra marks for being a hero.