Q.Would it be easier to drink water with a straw on the top of Mount Everest?

Pressure is defined as force divided by the area over which that force acts:

The SI unit of pressure is the pascal (Pa), defined as one newton of force spread over one square metre, $1\ \text{Pa}=1\ \text{Nm}^{-2}$. In chemistry, several other pressure units remain in everyday use and each converts to the pascal by a fixed factor: 1 atmosphere (atm) = 101325 Pa; 1 millimetre of mercury (mmHg) = 133.322 Pa; 1 bar = $10^5$ Pa; 1 torr = 133.322 Pa (numerically identical to the mmHg); 1 pound per square inch (psi) = 6894.76 Pa.

Atmospheric pressure and altitude. The atmosphere is not weightless -- the air pressure measured at any point is caused by the weight of the entire column of air sitting above it. At sea level this column is at its longest and heaviest, giving the highest pressure; climbing a mountain shortens the column of air above you, so atmospheric pressure measurably drops with altitude. This is exactly what a mercury barometer measures: it is open to the atmosphere at one end, and the height to which atmospheric pressure can push a column of mercury up the sealed tube rises and falls in step with atmospheric pressure -- a higher outside pressure pushes the mercury column higher, and a lower outside pressure lets it fall. …