K°P vs KP in equilibrium thermodynamics I'm having a little trouble with definitions. 

Here's a copy and paste from my hwk:

...K°P, and K°c have no units...Please enter the KP in 1/bar in  3 significant figures...

So these values even have different units, it's not a typo or anything. 

Given: aA+bB $=&gt;$ cC+dD

Is $$K°P=\frac {[C]^c[D]^d}{[A]^a[B]^b}$$ 
or is
$$KP=\frac {[C]^c[D]^d}{[A]^a[B]^b}$$

the question stated that K°P had no units, and the equation could be unitless if a+b=c+d, but that may not always be the case. 

Can somebody tell me which "KP" matches the definition, and also provide, or link the formula for the other "KP"? 

Sorry for asking such a trivial question but I'm having alot of trouble finding these definitions.

Thanks all.
The equilibrium constant should be dimensionless, it has to be to be used in equations such as the free energy for reaction at equilibrium 
$\Delta G^0_R = -RT\ln(K_p)$.

If the reaction is 
$\ce{\alpha A + \beta B \&lt;=&gt;\ \gamma C + \delta D} $
 if we write

$$K_p= \frac{P_A^{\alpha} P_B^{\beta}}{P_C^{\gamma}P_D^{\delta}} $$

where $P_a$ etc are partial pressures at equilibrium then $K_p$ is going to  have dimensions in general depending ion the values of $\alpha , \beta $ etc. as you state in your question.

In the past it was sort of implicitly assumed that each pressure was divided by 1 atm so then $K_p$ becomes dimensionless (or the units were simply ignored and numerical values used) but nowadays this is explicitly added so we obtain

$$K_p= \frac{\left(\frac{P_A}{P^0}\right)^{\alpha}  \left(\frac{P_B}{P^0}\right)^{\beta}}{\left(\frac{P_C}{P^0}\right)^{\gamma}\left(\frac{P_D}{P^0}\right)^{\delta}} $$

where $P^0 = 1 \pu{ atm}$  and so makes things dimensionless no matter what the values of $\alpha, \beta $ etc are but does not change any numerical value.

Although I have used partial pressures the same applies to concentrations $\ce{[A], [B]}$ etc where now each concentration is divided by  $\ce{[C^0]}$ where this is  $ \pu{1 mol/dm^3}$.

I'm not quite sure what your notation $K^0P$ etc. means but I suspect it refers to the two cases I have described. Hope this helps.