The answer iiiis... A: Group 8A, Period 1
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Here's why:</h3>
The way I found this doesn't have much thought or explanation--I just remember that helium and hydrogen are in period 1. The only answer choice with "period 1" is A.
200 is the answer let me know if you need anything
Answer: 996 mmHg
Explanation:
According to avogadro's law, 1 mole of every substance occupies 22.4 L at NTP, weighs equal to the molecular mass and contains avogadro's number
of particles.
According to the ideal gas equation:

P = Pressure of the gas = ?
V= Volume of the gas = 25.5 L
T= Temperature of the gas = 13°C = (273+13) K = 286K
R= Gas constant = 0.0821 atmL/K mol
n= moles of gas= 1.42
(760mmHg=1atm)
Thus pressure of this gas sample is 996 mm Hg.
Answer:
is a weak acid with a strong conjugate base 
is a weak base with a strong conjugate acid 
Explanation:
Weak acids do not completely dissociate in water to its distinctive ions, but instead forms conjugate bases; and ice versa with weak bases. The conjugate base has strong affinity for protons and vice versa.
I hope you found this explanation clear and easy to follow.