If the price per unit decreases by 20% during 2000-2004 and cost per unit increases by 20% during 2005-2010, then during how many number of years there is loss?

Let's calculate No of Units as Revenue / Unit price.

Per Unit cost as (Revenue - Profit ) / No of Units.

Costs Incurred = Revenue - Profit 

If there  is a percent 20 % increase in the cost price for year 2005-10 and the 20% decrease in price during 2000-2004. 

In that way, we calculate the table as follows.

The company will incur a loss if unit price is lesser than unit cost price.

Thus for 2000, 2001, 2003, 2004 and  2008 there will be net loss. For 5 years there was a loss.

Hence C is the correct answer.