I've selected in DS 160 B1/B2 instead of B2. I am going to travel to USA only for pleasure purpose. There is no business involved. Is this a problem, can this affect my application? will appreciate your help. I have got an interview in two weeks.
As far as I can tell, the US generally issues B-1/B-2 combination visas, even to applicants who have requested only a B-1 or B-2 visa, except in cases where the reciprocity policy is different for the different types. The reciprocity policy depends on your nationality, which you haven't disclosed, but you can look it up at U.S. Visa: Reciprocity and Civil Documents by Country.
If the reciprocity for your nationality is the same for all three types of visa, then requesting the combination visa should not affect your application, and you would probably get it even if you hadn't requested it. You might be asked about how likely it is for you to want to travel to the US for business in the future. If the reciprocity is different for the different types, then you might end up with a different duration of validity or a different visa reciprocity fee as a result. The interviewer may give you an opportunity to change the visa type if that is the case.
I had to apply for a US Visa this year (2019) simply because I had a long layover in Atlanta while travelling to Japan and back a month later.
I applied for the B1/B2 because I thought why not, if I was already going through all of the trouble and paying 160 USD for the paperwork. I detailed that I would only be around for a short while in this trip and would shop around Atlanta in the day I had to stay as a layover. Immigration procedure went on as normal, and in the interview I was simply asked the purpose of my trip, and the usual questions about how much connection I had to my home country (work, family, financial status, etc.) I ended up getting a 10 year B1/B2.
From this experience I don't think they mind much if you do B1, B2, or mixed B1/B2 as long as you're not at risk of staying illegally in the country.