The correct answer is D.
Echo refers to the sound that is heard when a sound wave is reflected back from a surface. An echo sound is made when a sound wave traveled through the air, hit a hard surface and get reflected back. Generally, hard surfaces reflect sound wave while soft surfaces absorb sound waves. Reflected sound waves are used in application of some devices that are used in range and direction finding.
A substance that is impenetrable by x-rays is described as being radiopaque.
Radiopaque substances will not allow x-rays and or other forms of radiations to pass through them.
Instead, they absorb or block the rays and when used in radiology, they appear white or light gray on photographic films.
Radiopaque materials are applied in generating ultrasound images and other forms of clinical procedures.
More on radiopaque materials can be found here: brainly.com/question/10583205?referrer=searchResults
621.4L
Explanation:
Given parameters:
Initial volume = 547L
Initial temperature = 331K
Final temperature = 376K
Unknown:
Final volume = ?
Solution:
The appropriate gas law to use is the Charles's law.
The Charles's law shows the relationship between the volume and temperature of a gas under constant pressure.
The law states that "The volume of a fixed of a gas varies directly as its absolute temperature if the pressure is constant".
Mathematically;
V₁ is the initial volume
T₁ is the initial temperature
V₂ is the final volume
T₂ is the final temperature
Since the unknown is the final volume, we make it the subject of the expression;
V₂ = 
V₂ = 621.4L
learn more:
Boyle's law brainly.com/question/8928288
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There are 4 electron pairs (3 bonding and 1 lone pair) so the angle is 107 degrees. The 4 electron pairs are repelled to give a tetrahedral arrangement but the molecule has a pyrimidal shape due to the lone pair.
