Montags and Clarisse's realtionship is weird. If she had not died I think they would have become a lot closer throughout the book. Clarisse seemed to bring out a different side of Montag. They way she would ask him questions and make things for him.
JKS stands for Java KeyStore. It is a repository of certificates (signed public keys) and [private] keys. You can export a certificate stored in a JKS file into a certificate file. You can use the keytool utility found in Java distributions to maintain your JKS trust and key repositories.
Apk is the android package. R.java (auto generated file) when compiled along with .class (java classes) generated .dex file but these files are not deployable. .dex files are then reprocessed along with manifest file, and other resources (mp3, video, image) and .apk file is generated. This file is deployable.