What is the velocity of sound in air?

The correct answer is option 1. 343 m/sec.

The velocity of sound in air depends on various factors, including temperature, humidity, and atmospheric pressure. However, under standard conditions (at sea level and at a temperature of 20 degrees Celsius or 68 degrees Fahrenheit), the velocity of sound in dry air is approximately 343 meters per second.

So, the correct option is: 343 m/sec.