Is 900 siver worth more or less than 925 silver?

No, it's not more valuable from a scrap standpoint. Silver is marked according to how much actual silver it contains, up to 1000, which would be pure silver. 900 silver contains 900 units of elemental silver, and 100 units something else, usually copper or nickel. 925 silver contains 925 units of elemental silver and 75 units something else. 925 silver has more silver than 900 silver, thus, for scrap purposes, it is worth more.

However, for decorative or antique value, 900 silver can be more valuable than 925 silver. 900 silver, if it is antique or a highly-sought decorative item, could fetch a much higher price than an ordinary or ugly 925 silver item. Take your items to a jewelry store that doesn't buy scrap gold or silver and ask them if your item has any resale value.