Answer:
 3.91 moles of Neon
Step-by-step explanation:
According to Avogadro's Law, same volume of any gas at standard temperature (273.15 K or O °C) and pressure (1 atm) will occupy same volume. And one mole of any Ideal gas occupies 22.4 dm³ (1 dm³ = 1 L).
Data Given:
 n = moles = ???
 V = Volume = 87.6 L
Solution:
 As 22.4 L volume is occupied by one mole of gas then the 16.8 L of this gas will contain....
 = ( 1 mole × 87.6 L) ÷ 22.4 L
 = 3.91 moles
2nd Method:
 Assuming that the gas is acting ideally, hence, applying ideal gas equation.
 P V = n R T ∴ R = 0.08205 L⋅atm⋅K⁻¹⋅mol⁻¹
Solving for n,
 n = P V / R T
Putting values,
 n = (1 atm × 87.6 L)/(0.08205 L⋅atm⋅K⁻¹⋅mol⁻¹ × 273.15K)
 n = 3.91 moles
Result:
  87.6 L of Neon gas will contain 3.91 moles at standard temperature and pressure.