The correct answer is option 3: 1 and 3 only.

1. Rigvedic Aryans used the coat of mail and helmet in warfare whereas the people of Indus Valley Civilization did not leave any evidence of using them.

The Rigvedic Aryans were a nomadic people who were primarily engaged in warfare and cattle-rearing. They were skilled in using weapons such as bows and arrows, spears, and swords. The Rigveda mentions the use of coats of mail and helmets in battle. The people of the Indus Valley Civilization, on the other hand, were primarily engaged in trade and agriculture. There is no evidence of them using armor or helmets in warfare.

2. Rigvedic Aryans knew gold, silver and copper whereas Indus Valley people knew only copper and iron.

This statement is incorrect. The people of the Indus Valley Civilization were skilled in metallurgy and used a wide range of metals, including copper, bronze, lead, and tin. They also used silver for ornaments and decorations. Gold was also known to them, but it was not as commonly used as in later periods. The Rigvedic Aryans were also familiar with a range of metals, including gold, silver, and copper.

3. Rigvedic Aryans had domesticated the horse whereas there is no evidence of Indus Valley people having been aware of this animal.

The Rigvedic Aryans were known for their domestication of horses, which gave them a significant advantage in warfare and helped them to expand their territories. The horse is frequently mentioned in the Rigveda, and chariot warfare was an essential aspect of their military strategy. In contrast, there is no evidence of the people of the Indus Valley Civilization being aware of the horse or using it for any purpose.

In conclusion, option 3 is the correct answer, as the statements 1 and 3 are correct, while statement 2 is incorrect.