Which of the following statements is true?
Electrons are found in the nucleus.
A piece of magnesium is made only of magnesium atoms.
All 118 elements occur naturally on Earth.
Protons and neutrons orbit the nucleus of an atom.

in the given question, the partial pressure is calculated by using the ideal gas equation, that is, pv = nrt

here, p is pressure, v is volume = 25 l, n is number of moles = 0.0104 moles, r is gas constant = -0.0821 l.atm / mol.k

t is temperature = 273 k

p = nrt / v

p = (0.0104 mol × 0.0821 l.atm / mol.k × 273 k) / 25 l

= 0.0093 atm

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your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.