Electrocardiography is a medical diagnostic

techniques, ultrasonic waves are used to construct the image of the heart, for

monitoring a nuclear reactor.

The frequency of an ultrasonic wave is greater than 20,000Hz and equal to 107Hz. These waves are not audible to a human ear but they can be heard by animals and birds.

Bats can produce ultrasonic waves by flapping their wings.
They can also detect these waves.these waves produced by the bats after reflection from the obstacles like building guide them to  remain away from the obstacles during night with the help of ultrasonic waves.

By detecting reflection of ultrasonic sound bats understands position and type of prey of any obstacle in way

Sound above frequency of 20000Hz is ultrasound or ultrasonic sound

By producing ultrasonic sound which are sent to the prey and reflected back, to find the exact location of the prey and catch them.

Ultrasound beam is more directional and can be aimed towards any target just like a torch. Thus ultrasonic waves remain undeviated over long distances

Ultrasound waves can penetrate into matter to a large extent because they have very high frequency. They have frequency higher than 20,000Hz.

Ultrasound has higher frequency than the audible range sound, and thus it has shorter wavelength. Due to this short wavelength, it becomes easy for it to interact(reflect, disperse) from small objects in its path.

Among the above, high frequency is property of ultrasound.

Ultrasonic waves are not harmful but just humans cant hear those frequency.

Ultrasonics, vibrations of frequencies greater than the upper limit of the audible range for humans, that is, greater than $20kHz$.

The frequencies used in ultrasonic diagnosis are in the range of 1 to 10 MHz. The speed of sound waves in the tissues of the human body averages about 1540 m/s (close to that for water). So, the wavelength of a 1 MHz wave is about $λ = v/f = 1540/1∙106 = 1.5∙10–3 m = 1.5 mm$.

Ultrasound can be used in 

Infrasound, sometimes referred to as low-frequency sound, is sound that is lower in frequency than 20 Hz or cycles per second, the "normal" limit of human hearing. So 5Hz is infrasonic.

Audible range of frequency for human ear is  $20 \ Hz$ to $20 \ kHz$. Humans cannot hear sounds having frequency other than this range.
Sounds having frequency lower than $20 \ Hz$ are known as infrasonic sounds and that having frequency greater than $20 \ kHz$ are known as ultrasonic sounds. Thus, humans can neither hear infrasonic nor ultrasonic sounds.

Aquatic animals as dolphins also use ultrasound to catch their prey. Statement is true.

The options in the question are given unnecessarily. It can be a direct question.
Below are the applications of ultrasound.

• Ultrasound has been used in a variety of clinical settings, including obstetrics and gynecology, cardiology and cancer detection. The main advantage of ultrasound is that certain structures can be observed without using radiation. Ultrasound can also be done much faster than X-rays or other radiographic techniques. 
• Ultrasound is well known to have a significant effect on the rate of various processes in the food industry. Using ultrasound, full reproducible food processes can now be completed in seconds or minutes with high reproducibility, reducing the processing cost, simplifying manipulation and work-up, giving higher purity of the final product, eliminating post-treatment of waste water and consuming only a fraction of the time and energy normally needed for conventional processes. Several processes such as freezing, cutting, drying, tempering, bleaching, sterilization, and extraction have been applied efficiently in the food industry. The advantages of using ultrasound for food processing, includes: more effective mixing and micro-mixing, faster energy and mass transfer, reduced thermal and concentration gradients, reduced temperature, selective extraction, reduced equipment size, faster response to process extraction control, faster start-up, increased production, and elimination of process steps. Food processes performed under the action of ultrasound are believed to be affected in part by cavitation phenomena and mass transfer enhancement. 
• Ultrasound is used in the synthesis of nanostructured materials.
• Devices limited to low ultrasonic frequencies, have a number of industrial applications, including drying, ultrasonic cleaning, and injection of fuel oil into burners. 

ultrasound is used for removing kidney stones.when ultrasound are targeted on such stone,the stones start vibrating at high frequency.the stone due to this vibratory motion. Breakdown into fine particles.ultrasounds and infrasounds are not audible to man.ultrasound have frequency more than 20kHz.a doorbell can produce an audible sound. Infrasound have frequency below 20Hz, X is ultrasound. Y is infrasound, Z is audible sound.

Frequencies higher than 20 kHz are called ultrasonic sound
or ultrasound. Ultrasound is produced by dolphins, bats and porpoises. Moths of certain families have very sensitive hearing equipment. These moths can hear the high frequency squeaks of the bat and know when a bat is flying nearby, and are able to escape capture. Rats also play games by producing ultrasound.

having a frequency above the human ear's audibility limit of about 20,000 hertz —used of waves and vibrations