Question

As we go up in the atmosphere wii the velocity of sound be the same

Answer 1

It depends on where in the atmosphere you are talking about. The speed of sound depends almost exclusively on temperature and the average molecular mass of the air.

In the troposphere, as a general rule, the composition of the air stays fairly constant other than some variation of water vapor content, and, in general the temperature decreases as altitude increases, though there can be temperature inversion layers. The speed of sound in air is very close to proportional to the square root of the thermodynamic temperature. Nominally, the temperature of the troposphere drops at a constant rate with respect to altitude. The temperature and speed of sound are nominally constant, independent of altitude in the lower parts of the stratosphere. In the middle and upper parts of the stratosphere, the temperature and speed of sound increase with altitude.

Nominally at sea level the speed of sound is about 340 m/s and in the lower stratosphere is about 295 m/s.

Does the speed of sound depend in any way at all on the density or pressure of the air? Yes, however, the oddities in speed of sound associated with the pressure are pretty much completely offset by the oddities in the dependence on the density, except for the temperature dependence. Therefore, you are wasting your time due to canceling effects if you try to determine the speed of sound based on the density and pressure.