Which of the following reactions are exothermic?

 

$$\begin{gathered} 1) C + O2 → CO2 \\ 2) 2Mg + O2 → 2MgO \\ 3) CuSO4 + 5H2O → CuSO4.5H2O \\ 4) All the above \end{gathered}$$

The   first   model   of   atom   was proposed   by   J.   J.   Thomson   in 1898.According  to  this  model,  the positive   charge   of   the   atom   is uniformly   distributed   throughout the  volume  of  the  atom  and  the negatively  charged  electrons  are embedded  in  it  like  seeds  in  a watermelon.    This    model    was picturesquely  called  plum  pudding model of the atom

Isotopes-These  are  atoms  of  the elements  having  the  same  atomic number but different mass number.,  Isobars-These  are atoms of same mass number but different atomic  number.,  Isotones-These are  atoms  of  different  elements having same number of neutrons.

Atomic  number  is  the  fundamental properties  of  an  element.  Every atom  is  identified  by  its  unique atomic  number.  Atomic  number  is equal  to  the  number  of  protons present in an atom of the element.

Water  is  neutral  and  has  a  pH value  of  7  and  because  here it  is multiple distilled water, it would be very near to seven

In Burning of coal, burning of wood and Heating of Potassium Chlorate there will be some sort of chemical change, but Heating of a Platinum crucible is a physical change.

Semiconductors are the basic materials used in the present solid state electronic devices like diode, transistor, ICs, etc. 2. Lattice structure and the atomic structure of constituent elements decide whether a particular material will be insulator, metal or semiconductor. Semiconductors are elemental (Si, Ge) as well as compound (GaAs, CdS, etc.). Silicon, Germanium, Gallium Arsenide are semiconductors, but Quartz is an insulator.