as like in some advertisement they display buy this product so we will give 1% or 4% to charity or any social service.
but in my view its unethical they are just increasing their product sale n if that sale will happen then they will give a little amount for any social cause.

It's definitely irrational to respond to someone advertising like that, you could just donate the 1% yourself, but a lot of advertisement is like that.

The big question is what effect it has on the person buying the product. They'll think of it as giving to charity. It could keep them from donating to charity, since they feel like they've donated by buying the product. It could be that it has no effect, in which case it's good. Even 1% will make a big difference if it's a good charity. It could cause them to donate to charity more, since buying it makes them think of themselves as more of a philanthropist.

From what I've heard, I think it might keep them from donating in the short term, but make them donate more in the long term, so it's good overall.

Let me put one of my old ideas forward once again: If
1) you own a business
2) you're going to donate a big portion of your profits (as would any good utilitarian)

then, you might you might as well make that an official promise to your customers. Then, you can turn your generosity into a selling point. That is, if you offer to donate 50% of your profit to charity, that will attract lots of extra customers. Your customers will buy more from you if they know they're contributing to a good cause, for example, the education of African children. The bottom line is: if you're donating profit to charity, let your customers know about it, and you will attract more customers and larger profits.

Now to defend this position against objections:
Objection 1 (by DanielLC): When customers consume your product, this will alleviate their guilt. This will discourage them from donating in the conventional fashion.
Response 1: Let us give the benefit of the doubt to your objection: let's assume that customers who consume our product donate less conventionally.

Well, charity isn't just about the amount of money. It isn't even mostly about how much money is donated. It's mostly about where the money is donated. Your customers don't know this. They might give their money to someone like The Seeing Eye. However, you have read Toby Ord's piece on the Seeing Eye and Fred Hollows. You know that money should go to Fred Hollows, rather than the seeing eye. In fact, it will be hundreds of times more effective if given there. What is important is that your customer has given some money to an effective charity by purhcasing your product.

So even if our customers donate a little less to charities such as the Seeing Eye, this is not very important. What is important is that our customer has been induced to donate to effective charities such as Fred Hollows'.

Well, if they are donating their %1 of profits for Moggy Yum-Yum Cat Food to a charity and the very fact that it is a point of product differentiation sort of makes me think that if I was the owner of No# 1 Kitty Crunch and I could out-bid them on a similair product with an equally just cause as my way of increasing product share then I would. So now we have two products on the market, one donating %1 and mine donating %5, therefor increasing the overall amount donated to charity when before there was none. Who knows, perhaps Moggy Yum-Yum might try and match me on %5 as well if I am threating their market share with my audacious and cunning plan of selling more cat food. Now, I don't imagine that the bidding war of charity sales driven motivation would increase very high at all because money donated beyond profit gained by the stunt would probably be minimal. So, I have no problem with it, people will continue buying cat food irregardless of charity donation stunt or not, just that if they are then at least they are doing something. However I don't believe that it would affect peoples sense of charity, because charity for most people means a personal sacrifice or giving up something of their own beyond what they would normally. Buying cat food is what they would already have done anyway, well, if they have a cat