What is the difference between the risks of an individual asset versus a portfolio of assets? What is single default correlation measure? If the average PD in a pool of 200 assets in 1.70 per cent and...

What is the difference between the risks of an individual asset versus a portfolio of assets? What is single default correlation measure? If the average PD in a pool of 200 assets in 1.70 per cent and joint default probability within similar assets class is 0.07 per cent, calculate the default correlation for the pool.