When does phenolphthalein turn pink? in the presence of a base in the presence of an acid when it is in a neutral solution when it is reacting with a metal

Answer : in the presence of a base

Explanation:

Phenophthalein is an acid base indicator which changes it's color. It turns pink when exposed to the pH of 8.2 that is basic in nature. It may turn purple when exposed to higher pH values. The color change occurs due to change in charge and shape of the phenophthalein molecules.  It remains colorless in acidic solutions. Therefore, it can be useful for detection of basic solutions.

the answer is (A) in the presence of a base

Explanation:

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