Question

The density of water at 4°C is supposed to be 1000 kg m^–3. Is it same at sea level and at high altitude?

Answer 1

At sea level, the pressure is around 1 atmosphere and at high altitude, the density of air reduces.
Pressure of liquid,
$$\begin{gathered} P=h\rho g, \\ \mathrm{where}\rho =\mathrm{density}\mathrm{of}\mathrm{fluid} \end{gathered}$$
The above equation shows that pressure depends on density. Therefore at 4^o​C, the density of water will be less at high altitude, compared to the density at sea level.