Hydrogen boils at 20k. what is the boiling point of hydrogen on the celsius scale

Celsius scale is related to kelvin scale by the following equation,

⁰C = K-273

°C = K-273  

So as here temperature is given in kelvin, so it can be converted into celsius as follows:

So 20 K = 20K-273 °C  

= -253 °C .

So, the 20 K temperature equals to -253 °C.

So , -253 °C is equals to  20 K or 20 K temperature equals to -253 °C.

d: the voltage of the secondary coil is less than that of the primary coil.

im not suree sorry if wrong

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.