PLEASE HELP! What type of reaction is the following?

3fe+4h2o=fe3o4+4h2

A. Synthesis
B. Decomposition
C. Single Replacement/Single Displacement reaction
D. Double Replacement/Double Displacement reaction

Two loudspeakers, 5.5 m apart and facing each other, play identical sounds of the same frequency. you stand halfway between them, where there is a maximum of sound intensity. moving from this point toward one of the speakers, you encounter a minimum of sound intensity when you have moved 0.33 m . assume the speed of sound is 340 m/s.part a) what is the frequency of the sound? part b) if the frequency is then increased while you remain 0.21 m from the center, what is the first frequency for which that location will be a maximum of sound intensity? express your answer to two significant figures and include the appropriate units.

Sunidhi made a study chart about changes in states of matter. which headings best complete the chart?

Which of the following best describes the circuit shown below?