How many of the carbon–carbon bonds in the compound have staggered conformers that are all equally stable?

Answer : The 3 carbons which are bonded to have equally stable staaggered conformers.

There are 3 identical atoms of hydrogens in 2-methylhexane molecule (refer attached figure)

Therefore any degree of rotation of 60 or 180 or 300 in C-C bond will give a stable conformer of the same energy.

The image is attached for the stable staggered conformation.

first let us lay out the formula for potential

and kinetic energy:

pe = mgh

ke = (mv^2)/2

where: m=mass, v=velocity, g=gravitational

acceleration, h=height

calculating for mass using the known values of

pe:

340j = m (9.81 m/s^2) (50ft) (1m/3.28ft)

m = 2.27 kg

the law of conservation of energy states that

energy is neither created nor destroyed. therefore, the change in kinetic

energy from 50 ft to 35 ft would be equal to the change in potential energy

from 50 ft to 35 ft. however it would be opposite in signs since one is losing

while other is gaining.

ke(35ft) – ke(50ft) = - [ pe(35ft) – pe(50ft]

ke(50ft) = 0 since the brick is initially at rest

ke(35ft) = 340j - 2.27kg (9.81 m/s^2) (35ft)

(1m/3.28 ft)

ke(35ft)

= 102.38 j

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.