Is it okay and safe to store pulses, grains, rice etc. in these containers? During coronavirus lockdown, I can't buy containers. But I've some empty boxes of Protinex powder like these: https://www.amazon.in/Protinex-400-g-Tasty-Chocolate/dp/B01MS489AE I guess it is made from metal.

So is it safe to store these things in it? Or it will be harmful to these things?
When storing nonperishable dry foods, such as pulses or grains or protein powder, you want the container to be reasonably airtight and impermeable, which that container appears to be. There aren't any other major considerations. Should be fine.