During an exothermic reaction; light and heat are released into the environment.
An exothermic reaction is one in which heat is released to the environment. This heat can be physically observed sometimes like in an a combustion reaction.
In an exothermic reaction, the enthalpy of the reactants is greater than the enthalpy of the products.
This heat lost is sometimes felt as the hotness of the vessel in which the reaction has taken place.
In conclusion, light and heat are released into the environment in an exothermic reaction.
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Light gates are more reliable. When using a manual stop watch, it is difficult to stop it at an exact time. A light gate is able to detect when an object passes through a 'gate' with the infrared transmitter and receiver.
Answer:

Explanation:
the variations in riser height or tread depth should not be grater than
that is equal to 9.5 mm but the maximum riser height should be the
but variation in riser height should not exceed to
. The minimum riser height should be 7 inches which is equal to the 178 mm