sand is a solid why it sand can be poured?

Sand is lots and lots of little solids (each grain of sand is a solid)

So if you put that one grain of sand in a container, it won't pour.

It's like saying if you put 100s of balls in a huge container, it will pour if the container is tipped. However it's not a liquid, just lots of little balls.

it's "Granulated"

Mercury is a solid too, and it is liquified.

Marbles are solids. Why can marbles be poured? It is more accurate to say INDIVIDUAL GRAINS of sand are solids, but not sand as a collection of grains.

Is a rock a solid? If I put enough rocks in a large enough container, can I not pour them out? The word "pour" doesn't refer to just liquids.

https://www.merriam-webster.com/dictionary/pour

Any solid cut down to small enough pieces can be poured. Take a tree and put it through a wood chipper, the tiny pieces that come out of the chipper are the same tree you put in, both solids, but the wood chips can be poured. Take a slab of concrete and bust it up with a sledgehammer, the small rocks and pebbles are still solids, but they can now be poured. Even been to a rock quarry? They bust up rocks, put the pieces on conveyor belts, and pour them into trucks, but grab a rock off that truck and it's still plenty solid. Ever used rock salt? It's just a bigger version of the normal table salt, but table salt is smaller grains and so can be poured much easier.

For the same reason, sugar, salt and rocks can be poured.

Each grain of sand is a solid. When you have multiple grains of sand (or something like salt) you can pour it because each grain moves individually (not attached to the other grains) and the multiple grains move freely

grain size

because unlike most solids, sand is quite small individually and only gains its strength and its ability to be poured when you have quite a lot of it. Sand is only considered a solid because of its incompressibility when you have a bunch of it.