Balanced or Unbalanced

K+2MgBr=KBr+Mg

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

What is the correct lewis dot structure for arsenic?

Before it was launched, a helium-filled balloon had a pressure of 201 kpa at a temperature of 27°c. at an altitude of 15,000 m, the pressure had decreased to 2.5 kpa and the temperature had dropped to -14 °c. the volume of the balloon increased to 59.3 m3. what is the original volume of the balloon? 13 m3 0.85 m3 0.077 m3 1.17 m3