Question

True or false, salt water contains at least 3.5 percent salts or minerals

Answer 1

True — average seawater is about 35 parts per thousand, i.e. ~3.5% dissolved salts (mostly NaCl).

Note: the term "salt water" can also cover brackish water (<3.5%) and hypersaline waters (>3.5%), so not every salty water body is exactly 3.5%.