Answer: Oxygen
Explanation:

As seen from the balanced equation:
2 moles of hydrogen combine with 1 mole of oxygen or 1 mole of hydrogen combine with 1/2 mole of oxygen.
According to Avogadro's law, equal volumes of gases contain equal number of molecules and hence equal number of moles.
Thus if x moles of both gases are present, x moles of hydrogen will combine with
moles of oxygen and
moles of oxygen will be left used and will be in excess.
The molarity of a Ba(OH)2 solution required to prepare a1.0 OH- solution is calculated as follows
write the equation for dissociation of Ba(Oh)2
that is,
Ba(Oh)2 -----> Ba^2+ + 2Oh-
by use of reacting ratio between Ba(Oh)2 to Oh which is 1:2 the molarity of Ba(oh)2 = 1.0/2 = 0.5 M
Answer: conversion of ice to steam
Explanation: Endothermic process is one in which energy is absorbed by the system.
Conversion of ice to steam is change of solid phase to gaseous phase, thus energy is required to break the strong inter molecular forces of attraction in solids to convert it into gaseous phase.
Conversion of steam to ice, conversion of steam to water and conversion of water to ice releases energy and are examples of exothermic processes.