The answer is B: elliptical. Spirals have arms so are not round, no such thing as circular, and irregular don't have simple geometric shapes
"A machine can decrease either the input force or the input distance needed to do a given amount of work" is the best statement that describes why a machine is useful.
Answer: Option D
<u>Explanation
:</u>
A machine is simply defined as a device that helps humans, helping them to transfer the required amount of force to compete any task, changing the direction of motion, increasing the magnitude of force to complete any task, reduce the time or distance needed to cover while performing any task.
Machines can be simple mechanical device or a combination of multiple mechanical or technical devices to reduce the amount of input force or increase the output.
Solid! The molecules in solid matter are arranged closely together and packed quite tightly to maintain a regular shape. Hope this helps!
C burning coal in a furnace
Answer : The enthalpy change for the decomposition of calcium carbonate is, 178.1 kJ/mol
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.
The given main reaction is,

The intermediate balanced chemical reaction will be,
(1)

(2)

(3)

(4)

Now we are reversing reaction 1 and then adding reaction 1 and 2, we get :
(1)

(2)

The expression for enthalpy of change will be,



Thus, the enthalpy change for the decomposition of calcium carbonate is, 178.1 kJ/mol