Asample of gas has an initial volume of 25 l and an initial pressure of 3.5 pa. if the pressure changes to 1.3 pa, find the new volume, assuming that the temperature remains constant.

Since you are provided with the pressure and initial volume and told a standard temperature, you should use the Combined gas law. This is (P1 V1)/ T1 = (P2 V2)/ T2 
STP is 273 k for temperature, so plug in the values. 
(3.5 Pa * 25 L)/ 273 K =1.3 Pa * X L)/ 273 K.
(this is the left side>)0.32051= 1.3 X/ 273.  Multiply both sides by 273 to get rid of it on the right, which leaves you with
87.4999 = 1.3 X. Divide both sides by 1.3 and there you go, 

67.308 L

No. an alpha particle is a pair of protons and a pair of neutrons, i.e. a helium

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf