Can I put washing powder and soap in my backpack abroad?

You can take it with you. Washing powder and soap are neither dangerous nor liquid, so they can be carried with you.

Articles prohibited from being carried or checked on international flights include:

Guns and ammunition, controlled knives, police equipment, inflammable and explosive substances (such as lighter gas, alcohol, paint, fireworks and firecrackers), corrosive substances, toxic substances and other dangerous goods.

As long as the capacity of the container does not exceed 100 ml, it can be used to hold liquid, gel and spray articles.

If the capacity of liquid container exceeds 100 ml, it should not be put in hand luggage, but should be checked in checked luggage.