alguien me puede ayudar en química por favor no trolls es de suma importancia

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.

What causes most sediment to wash or fall into a river

Asample of hydrated tin (ii) chloride (sncl2) has a mass of 4.90 g. when it is dehydrated, it has a mass of 4.10 g. which is the correct chemical formula for the hydrate? sncl2•2h2o          sncl2•4h2o          sncl2•6h2o