Answer is: (3) ionic and molecular.
Ionic compounds are made of ions held together with ionic bonds.
Ionic bond forms when a cation transfers its extra electron to an anion who needs it.
For example compound magnesium chloride (MgCl₂) has ionic bond (the electrostatic attraction between oppositely charged ions).
Magnesium (metal) transfers two electrons (became positive cation) to chlorine (became negative anion).
Molecular compounds are made up of molecules whose atoms are connected with covalent bonds.
Covalent bond is bond between nonmetals.
For example, molecule carbon monoxide CO has covalent bond.
Carbon (C) and oxygen (O) are nonmetals.
Carbon atom and oxygen atom are connected by a triple bond (six shared electrons in three bonding molecular orbitals) that is formed of two covalent bonds and one dative covalent bond.
Rutherford performed gold foil experiment to understand that how negative and positive particles could Co exist in an atom. He bombarded alpha particles on a 0.00004 cm thick gold foil.
He proposed a planetary model of the atom and concluded following results and demonstrated that,
1. An atom produces a line spectrum.
2. An Electron revolves around the nucleus without any orbits.
3. Since most of the particles passed through the foil undeflected it means that most of the volume occupied by an atom is empty.
4. An Atom as a whole is neutral.
5. The deflection of few particles on the foil suggested that there is center of positive particles in an atom called the nucleus of the atom.
6. The complete rebounce of few particles on the gold foil suggested that the nucleus is very dense and hard.
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25° C is the temperature required for the cell potential to be the standard cell potential
Answer: The empirical formula is 
Explanation:
If percentage are given then we are taking total mass is 100 grams.
So, the mass of each element is equal to the percentage given:
Mass of Na= 34.5 g
Mass of B= 16.4 g
Mass of O = 48.6 g
Step 1 : convert given masses into moles.
Moles of Na =
Moles of B =
Moles of O =
Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.
For Na = 
For B =
For O =
The ratio of Na: B: O= 1: 1: 2
Hence the empirical formula is
