I would say the correct answer would be Elements.
Answer:
Neutral carbon-14 contains six protons, eight neutrons, and six electrons; its mass number is 14 (six protons plus eight neutrons). These two alternate forms of carbon are isotopes.
I hope it's helpful!
Answer : The standard enthalpy of formation for nitro-methane is, -467.4 kJ
Explanation :
Enthalpy change : It is defined as the difference in enthalpies of all the product and the reactants each multiplied with their respective number of moles. It is represented as 
The equation used to calculate enthalpy change is of a reaction is:
![\Delta H^o_{rxn}=\sum [n\times \Delta H^o_f(product)]-\sum [n\times \Delta H^o_f(reactant)]](https://tex.z-dn.net/?f=%5CDelta%20H%5Eo_%7Brxn%7D%3D%5Csum%20%5Bn%5Ctimes%20%5CDelta%20H%5Eo_f%28product%29%5D-%5Csum%20%5Bn%5Ctimes%20%5CDelta%20H%5Eo_f%28reactant%29%5D)
The equilibrium reaction follows:

The equation for the enthalpy change of the above reaction is:
![\Delta H^o_{rxn}=[(n_{(CO_2)}\times \Delta H^o_f_{(CO_2)})+(n_{(H_2O)}\times \Delta H^o_f_{(H_2O)})+(n_{(N_2)}\times \Delta H^o_f_{(N_2)})]-[(n_{(CH_3NO_2)}\times \Delta H^o_f_{(CH_3NO_2)})+(n_{(O_2)}\times \Delta H^o_f_{(O_2)})]](https://tex.z-dn.net/?f=%5CDelta%20H%5Eo_%7Brxn%7D%3D%5B%28n_%7B%28CO_2%29%7D%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28CO_2%29%7D%29%2B%28n_%7B%28H_2O%29%7D%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28H_2O%29%7D%29%2B%28n_%7B%28N_2%29%7D%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28N_2%29%7D%29%5D-%5B%28n_%7B%28CH_3NO_2%29%7D%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28CH_3NO_2%29%7D%29%2B%28n_%7B%28O_2%29%7D%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28O_2%29%7D%29%5D)
We are given:


Putting values in above equation, we get:
![-709.2=[(2\times -393)+(3\times -286)+(1\times 0)]-[(2\times \Delta H^o_f_{(CH_3NO_2)})+(\frac{3}{2}\times 0)]](https://tex.z-dn.net/?f=-709.2%3D%5B%282%5Ctimes%20-393%29%2B%283%5Ctimes%20-286%29%2B%281%5Ctimes%200%29%5D-%5B%282%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28CH_3NO_2%29%7D%29%2B%28%5Cfrac%7B3%7D%7B2%7D%5Ctimes%200%29%5D)

Thus, the standard enthalpy of formation for nitro-methane is, -467.4 kJ
Oxygen is the correct answer hope this helps
<span>Welding in confined spaces or on stainless steel generates (B) Hexavalent Chromium a very toxic chemical. Hexavalent chromium are chemical compounds that has a chromium with an oxidation state of +6. It is commonly used in textile dyes and wood preservation to avoid corrosion and conversion coatings.</span>