Opposite pairs form ionic bonds, due to this the answer is D - Li and Br; They have unlike charges.
2 NH3+ 2 O2 —> 2 NO+ 3 H2O
That's why it's important for you to use water wisely and not to waste it. When you waste water, you're taking water that other people might need. But when you use water carefully, you leave more water for other people to use. It is also important to use water carefully because our weather can be unpredictable.
Moles = mass / molar mass
molar mass of O2 is 32
therefore moles = 72/32
= 2.25 moles
