Questions

Herodotus, a Greek author written the first history book in 5th century B.C.

No improvement required. Sentence is idiomatically correct.

Tradestation is owned by its parent organization Monex Group, Inc.

Judicial branch is one among the three branches of the government. 

Supreme court, the magistrate (local) and municipal (city) courts are there in the judicial branch.

The Judicial branch interprets the laws.

Joseph Priestley and Carl Wilhelm Scheele both independently discovered oxygen in the year 1774, but Priestly is usually given credit for the discovery.

Secondary storage therefore needed because it is non-volatile, meaning it retains its contents without the need for a power supply. It also has the large storage capacity needed to store the operating system and all the programs and files needed by a modern computer system.